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Citation: Ahn, S.-Y.; Bae, G.-E.; Park,
S.-Y.; Yeo, M.-K. Differences in the
Clinical and Molecular Profiles of
Subungual Melanoma and Acral
Melanoma in Asian Patients. Cancers
2023,15, 4417. https://doi.org/
10.3390/cancers15174417
Academic Editor: Nicolas Dumaz
Received: 4 August 2023
Revised: 1 September 2023
Accepted: 1 September 2023
Published: 4 September 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
cancers
Article
Differences in the Clinical and Molecular Profiles of Subungual
Melanoma and Acral Melanoma in Asian Patients
So-Young Ahn 1,† , Go-Eun Bae 2, †, Seung-Yeol Park 3, * and Min-Kyung Yeo 2,*
1Department of Rehabilitation Medicine, Chungnam National University School of Medicine,
Daejeon 35015, Republic of Korea; asyoung@cnuh.co.kr
2Department of Pathology, Chungnam National University School of Medicine, Daejeon 35015, Republic of Korea;
goeunbae@cnuh.co.kr
3Department of Life Sciences, Pohang University of Science and Technology (POSTECH),
Pohang 37673, Gyeongbuk, Republic of Korea
*Correspondence: seungpark@postech.ac.kr (S.-Y.P.); mkyeo83@gmail.com (M.-K.Y.);
Tel.: +82-42-280-7196 (M.-K.Y.); Fax: 82-42-280-8199 (M.-K.Y.)
†These authors contributed equally to this work.
Simple Summary:
Melanoma is a type of skin cancer that develops from melanocytes (the cells that
give the skin its brown color). Subungual melanoma (nail melanoma) is a rare type of malignant
melanoma that arises beneath the nails. Subungual melanoma has been categorized as a type of acral
melanoma, which occurs on the hands and feet. Using a genetic study, we found that subungual
melanoma showed molecular features that were different from those of acral melanoma. Subungal
melanoma had a frequently mutated gene, named G protein subunit alpha Q. Patients with subungual
melanoma show better survival than patients with acral melanoma. We suggest that subungual
melanoma should be considered as a type of melanoma that is separate from acral melanoma.
The genetic evaluation of subungual melanoma is important for advanced cancer patients, so that
appropriate targeted therapy may be selected.
Abstract:
Subungual melanoma (SUM) is a rare type of malignant melanoma that arises beneath
the nails. SUM is categorized as a type of acral melanoma (AM), which occurs on the hands and
feet. SUM is an aggressive type of cutaneous melanoma that is most common among Asian patients.
Recent studies reveal that SUM and AM might have different molecular characteristics. Treatment
of melanoma relies on analysis of both clinical and molecular data. Therefore, the clinical and
molecular characteristics of SUM need to be established, especially during metastasis. To define
the mutation profiles of SUM and compare them with those of AM, we performed next-generation
sequencing of primary and metastatic tumors of SUM and AM patients. Subungual location was
a better independent prognostic factor than acral location for better overall survival (p= 0.001).
Patients with SUM most commonly had the triple wild-type (75%) driven by GNAQ (58%) and KIT
(25%) mutations, whereas patients with AM had BRAF (28.6%) and RAF (14.3%) molecular types of
mutations. Single-nucleotide variations (SNVs) were more common in SUM than in AM, whereas
copy number alterations (CNAs) were more common metastatic lesions of AM. Metastatic tumors in
patients with SUM and AM showed increases in CNAs (43% and 80%, respectively), but not in SNVs.
The number of CNAs increased during metastasis. When compared with AM, SUM has distinct
clinical and molecular characteristics.
Keywords: subungual melanoma; acral melanoma; next-generation sequencing; Asian
1. Introduction
Subungual melanoma (SUM) is categorized as a subtype of acral melanoma, which
occurs on the hands and feet. SUM is a cutaneous malignant melanoma that arises from
structures within the nail apparatus. Although SUM is a rare variant of melanoma in
Cancers 2023,15, 4417. https://doi.org/10.3390/cancers15174417 https://www.mdpi.com/journal/cancers
Cancers 2023,15, 4417 2 of 15
Caucasians (1–3%) [
1
], it is much more prevalent in Asian and African people with dark-
pigmented skin (10–75% of melanoma cases) [
2
]. SUM is the most common cutaneous
melanoma in Asian patients [3].
Recently, several studies showed that SUM and AM have different clinical and molecu-
lar characteristics. SUM and AM show different genetic signatures and different frequencies
of mutated genes [
4
,
5
]. AM appears to have little or no relation to ultraviolet radiation
(UVR); however, SUM has a UVR-related mutational signature [
5
,
6
]. AM is an aggressive
type of melanoma with a poor prognosis; SUM is also thought to have a poor prognosis [
2
].
However, the 5-year survival rates for SUM patients range from 40% to 100%, depending on
the clinical stage at the time of diagnosis. Some cases of SUM are diagnosed at an advanced
stage, because it is often difficult to differentiate SUM from benign pigmented lesions of the
nails [
7
,
8
]. Treatment options for SUM patients are controversial and include amputation
or wide local excision of SUM tumors. This range of treatment options is due to the lack of
comprehensive analysis of the clinicopathologic features of SUM and the survival rates of
SUM patients, which makes clinical management difficult [9].
A few studies have been carried out to validate the molecular profiles of SUM. How-
ever, the number of patients enrolled in those previous studies have been limited. Some
patients with SUM have not been evaluated separately from AM, and such studies validated
only a few oncogenes, including BRAF mutations.
In the current study, we enrolled patients with SUM who had attended a single insti-
tution for 15 years and conducted next-generation sequencing (NGS) targeting 170 cancer-
related genes, using primary and metastatic tumors of SUM and AM. Our hypothesis was
that SUM and AM show distinct molecular characteristics in primary tumors and might
have different genetic alteration during metastasis. The validation of the genetic changes
in metastatic lesions is challenging, because targeted treatment and immunotherapy is
indicated for advanced stages of melanomas. Treatment of melanoma relies on both clinical
and molecular information to select appropriate surgical and therapeutic management.
A better understanding of the distinct clinical and molecular characteristics of SUM is
required to develop improved care pathways for melanoma patients.
2. Materials and Methods
2.1. Patients
Based on clinical photographs and medical records, 42 patients with SUM and 64 pa-
tients with AM were selected from the database of patients diagnosed with melanomas
between 1 January 2008 and 31 December 2022 at the Chungnam National University Hos-
pital, Daejeon, South Korea. The clinical data included age, sex, the location of the tumor,
lymph node metastases, and distant metastases (Table 1). Survival curves for patients
who died from melanoma were determined, based on data obtained from the medical
records. Slides of biopsies or excised SUM and AM tumors were reviewed by two of the
authors who are pathologists (M.-K.Y. and G.-E.B.). They collected the following data: the
histopathologic subtype, the Breslow thickness of the tumors, ulceration, and the mitotic
rate (mitotic count/mm
2
). The stages of the tumors were determined on the basis of the
most recent classifications set out in 8th edition of the staging manual of the American Joint
Committee on Cancer (AJCC) [10].
This retrospective study was approved by the Chungnam National University Hospital’s
institutional review board (IRB file no. CNUH 2020-09-015), which waived the requirement
for informed consent. All samples were provided by the Biobank of the Chungnam National
University Hospital, which is a member of the Korea Biobank Network.
Cancers 2023,15, 4417 3 of 15
Table 1. List of selected genes of NGS targeted cancer-related genes.
Abbreviation Gene Name
GNAQ G protein subunit alpha Q
KIT KIT proto-oncogene receptor tyosine kinase
BRAF V-raf murine sarcoma viral oncogene homolog B1
RAS Rat sarcoma virus
NRAS Neuroblastoma RAS viral oncogene homolog
KRAS Kirsten rat sarcoma virus
HRAS Harvey rat sarcoma viral oncogene homolog
NF1 Neurofibromin 1
CTNNB1 Catenin beta-1
ATM Ataxia telangiectasia mutated
CDK4 Cyclin-dependent kinase inhibitor 4
MDM2 Murine double minute 2
PDGFRA Platelet derived growth factor receptor alpha
CCND2 Cyclin D2
PIK3CA Phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha
TERT Telomerase reverse transcriptase
CDKN2A Cyclin-dependent kinase inhibitor 2A
CDKN2B Cyclin-dependent kinase inhibitor 2B
MYC Myelocytomatosis oncogene
MKRN1 Makorin ring finger protein 1
NOTCH2 Neurogenic locus notch homolog protein 2
PTEN Phosphatase and tensin homolog
FGF19 Fibroblast growth factor 19
FGF3 Fibroblast growth factor 3
2.2. Tissue Samples and NGS
DNA/RNA was extracted from formalin-fixed paraffin-embedded (FFPE) tissues
obtained from 16 patients with SUM and 7 patients with AM. Somatic alterations were
analyzed quantitatively by the NGS targeting of 170 cancer-related genes (insufficient
DNA/RNA was extracted from FFPE-tissue samples from the excluded patients). DNA
and RNA were isolated from 20
µ
m sections of FFPE-tumor-tissue samples using a sterile 26-
gauge needle and the RecoverAll
™
Multi-Sample RNA/DNA Isolation Workflow (Ambion,
Austin, TX, USA). Each tumor component was obtained by manual microdissection. DNA
and RNA were extracted for library preparation. For each case, normal control tissue was
dissected from an adjacent non-malignant region. DNA and RNA were quantified using
a Qubit 2.0 fluorometer (Thermo Fisher Scientific, Waltham, MA, USA). Libraries were
generated from 10 ng of DNA or RNA per sample, using the IonAmpliSeq
™
Kit for Chef
DL8, the Ion 540 Chef kit, and the Ion S5
™
Chef system (all from Thermo Fisher Scientific).
Sequencing was performed using the Ion S5 sequencer and Ion 540 chips (Thermo
Fisher Scientific). Sequence data analysis was performed using commercial pan-cancer
Oncomine Comprehensive Assay version 3, Torrent Suite version 5.10.2, and Ion Reporter
version 5.6 (Thermo Fisher Scientific). The Oncomine panel enabled analysis of variations
in 170 genes, including copy number alterations (CNAs) in 47 genes and fusion drivers in
51 genes (Supplementary Table S2). Abbreviations of selected genes from the panel are
described in Table 1. The workflow was created by adding a custom hotspots Browser
Extensible Data file to report mutations of interest and a custom CNA baseline using the
manufacturer’s default workflow, as previously described [11,12].
ANNOVAR software (http://www.openbioinformatics.org/annovar, accessed on 10
February 2023) was used for the functional annotation of the identified single-nucleotide
variations (SNVs) to investigate their genomic locations and variations [
13
]. To eliminate
error artifacts, sequence data were confirmed visually using the Integrative Genomics
Viewer. This workflow identified SNVs and indels with a variant allele fraction as low as
1%. Based on the results of a feasibility study, the variant allele fraction threshold was set
at 2%.
Cancers 2023,15, 4417 4 of 15
Somatic SNVs/indels that passed filtering for gain-of-function genes were considered
gain-of-function if they occurred at predefined hotspot residues targeted by the Oncomine
panel. Somatic variants of loss-of-function genes (oncogenes) were considered loss-of-
function when deleterious (nonsense or frame-shifting) changes occurred at a predefined
hotspot residue. Copy number analysis was performed using the copy number module
within the previously mentioned Ion Reporter system workflow. If the copy numbers
of target genes were
≥
4, they were considered to be amplifications. Additionally, if the
copy numbers of target genes were
≤
1, they were considered to be deletions. Somatic
CNAs were considered for potential actionability analysis when they were concordant
with alteration (amplifications or deletions) predicted by Oncomine analysis. Somatic gene
fusions were considered for actionability analysis when they represented known gene
fusions listed in the Mitelman database (National Cancer Institute, Bethesda, MD, USA) or
were determined by Oncomine analysis, or when they involved known 3
0
or 5
0
drivers with
novel partners. These prioritized variants were associated with potential actionability using
the Oncomine database. For each patient, the “most actionable” alteration was identified
based on the following criteria: (i) variants referenced in Food and Drug Administration
(FDA) drug labels; (ii) variants referenced in National Comprehensive Cancer Network
(NCCN) treatment guidelines for the patient’s cancer type; (iii) variants referenced in
an NCCN guideline for another cancer type; and (iv) variants referenced as inclusion
criteria in a clinical trial. Actionable variants were identified by manual curation of FDA
labels and NCCN guidelines, as well as by keyword searches and manual curation of
clinical trial records in the TrialTrove database [
11
]. The genetic variants identified were
interpreted and categorized as “pathogenic”, “likely pathogenic”, “variant of unknown
significance”, “presumed benign,” or “benign”, based on clinical significance according
to ClinVar-indexed variants (National Center for Biotechnology Information, USA) [
12
].
When assessing the mutation frequency of individual genes, “pathogenic” and “presumed
pathogenic” were counted as mutations, while “benign” “presumed benign”, and “variants
of unknown significance” were excluded.
2.3. Statistical Analysis
The Pearson
χ
2 test or Fisher’s exact test were used (as appropriate) to compare
the baseline characteristics of the subgroups and to compare categorical variables. For
univariate analysis, overall survival curves were generated using the Kaplan–Meier method
and analyzed using the log-rank test. Multivariate survival analysis was performed using
a Cox proportional hazards regression model in which age, stage, and subungual location
were entered as covariates. p< 0.005 was considered significant. All statistical analyses
were performed using SPSS version 26.0 for Windows (SPSS, Inc., Chicago, IL, USA).
3. Results
3.1. Characteristics of Patients with SUM
The baseline demographic and clinical characteristics of the 42 SUM patients are listed
in Supplementary Table S1. All SUM patients (20 men and 22 women) were Asian (Korean),
with a mean age of 55.7 (1–91) years. Twenty-nine (69.0%) SUM patients had fingernail
involvement and 13 (31.0%) had toenail involvement. The mean size of the SUMs was
1.2 cm (0.2–4 cm). Twelve patients (28.6%) had in situ melanomas. In addition, 12 (28.6%)
patients had tumors with a Breslow thickness <1 mm; four (9.5%) had tumors between
1 and 2 mm thick; five (11.9%) had tumors between 2 and 4 mm thick; and nine (21.4%)
had tumors >4 mm thick. Regarding the stages of disease, 12 patients (28.6%) had stage
0 disease, 11 (26.2%) had stage I disease, 12 (28.6%) had stage II disease, six (14.3%) had
stage III disease, and one (2.4%) had stage IV disease (based on the AJCC cancer-stage
group definition). Eleven SUM patients (26.2%) had histological ulceration. The mean
tumor mitotic rate/mm
2
was 3 (0–22/mm
2
). Seven SUM patients (16.7%) had lymph node
involvement and one (2.4%) had distant metastasis at the time of diagnosis. Five patients
(11.9%) had a history of trauma at the site of melanoma. Twelve patients (28.6%) received
Cancers 2023,15, 4417 5 of 15
chemotherapy, including targeted molecular agents; 11 (26.2%) received immunotherapy;
and three (26.2%) received radiotherapy during follow-up after diagnosis of SUM.
3.2. Differences in the Clinicopathologic Characteristics of Patients with SUM or AM
Differences in the clinicopathologic characteristics of the tumors in 42 patients with
SUM and 64 patients with AM, including in situ lesions, are listed in Table 2. Patients with
SUM were younger (mean age, 55.7 years) than those with AM (67.3 years) (p= 0.009).
The majority of primary SUMs developed on the nails of the hands (69%), in contrast to
primary AMs, which mostly developed on the sole of the foot (81.3%) (p< 0.0001). The
depth of SUM tumor invasion was shallower (the most frequent Breslow thickness was
<1 mm (28.6%)) than that of AM (the most frequent Breslow thickness was >4 mm (29.7%))
(p= 0.037). The stages of SUM were earlier than those of AM, with advanced tumors (stages
III-IV) reported less often for SUM (16.7%) than for AM (18.8%) (p= 0.016). More patients
with SUM (11.9%) reported prior traumatic events; no patient with AM reported a prior
traumatic event (p= 0.005). Loco-regional recurrence was less common in patients with
SUM (4.8% for SUM patients compared with 17.2% for AM patients), but this difference
was not statistically significant (p= 0.056). There were no significant differences related to
sex, lymph node, or distant metastases at the time of surgery or during follow-up (
p= 0.810
,
0.944, 0.821, 0.145, and 0.622, respectively).
Table 2.
Differences in the clinic-pathologic features of subungual (n = 42) and acral (n = 64)
melanomas including in situ lesions.
No. (%) Subungual Acral p
Sex 0.810
Male 52 (49.1) 20 (47.6) 32 (50.0)
Female 54 (50.9) 22 (52.4) 32 (50.0)
Age (years) 0.009
≤63 49 (46.2) 26 (61.9) 23 (35.9)
>63 57 (53.8) 16 (38.1) 41 (64.1)
Tumor location 0.000
Upper 41 (38.7) 29 (69.0) 12 (18.8)
Lower 65 (61.3) 13 (31.0) 52 (81.3)
Invasion of the dermis 0.004
In situ melanoma 17 (16.0) 12 (28.6) 5 (7.8)
Invasive melanoma 89 (84.0) 30 (71.4) 59 (92.2)
Breslow thickness 0.037
In situ 17 (16.0) 12 (28.6) 5 (7.8)
<1 mm 27 (25.5) 12 (28.6) 15 (23.4)
1.01–2.00 mm 15 (14.2) 4 (9.5) 11 (17.2)
2.01–4.00 mm 19 (17.9) 5 (11.9) 14 (21.9)
>4.00 mm 28 (26.4) 9 (21.4) 19 (29.7)
Lymph node metastasis
at the time of diagnosis 0.944
Absent 88 (83.0) 35 (83.3) 53 (82.8)
Present 18 (17.0) 7 (16.7) 11 (17.2)
Distant metastasis at
the time of diagnosis 0.821
Absent 103 (97.2) 41 (97.6) 62 (96.9)
Present 3 (2.8) 1 (2.4) 2 (3.1)
Stage group 0.016
0 17 (16.0) 12 (28.6) 5 (7.8)
I–II 70 (66.0) 23 (54.8) 47 (73.4)
III–IV 19 (17.9) 7 (16.7) 12 (18.8)
Immunotherapy 0.696
Not carried out 76 (71.7) 31 (73.8) 45 (70.3)
Carried out 30 (28.3) 11 (26.2) 19 (29.7)
Cancers 2023,15, 4417 6 of 15
Table 2. Cont.
No. (%) Subungual Acral p
Trauma 0.005
Absent 101 (95.3) 37 (88.1) 64 (100.0)
Present 5 (4.7) 5 (11.9) 0 (0.0)
Ulceration 0.226
Absent 71 (67.0) 31 (73.8) 40 (62.5)
Present 35 (33.3) 11 (26.2) 24 (37.5)
Loco-regional
recurrence 0.056
Absent 93 (87.7) 40 (95.2) 53 (82.8)
Present 13 (12.3) 2 (4.8) 11 (17.2)
Distant metastasis
during the follow-up 0.622
Absent 78 (73.6) 32 (76.2) 46 (71.9)
Present 28 (26.4) 10 (23.8) 18 (21.6)
Differences in the clinicopathologic characteristics of the tumors in 30 patients with
SUM and 59 patients with AM with invasive melanoma are listed in Table 3. The majority
of primary SUMs developed on the nails of the hands (60%), in contrast to 16.9% of
primary AMs (p< 0.0001). More patients with SUM (13.3%) reported prior traumatic
events; no patient with AM reported a prior traumatic event (p= 0.004). Patients with
SUM tended to be younger than those with AM (p= 0.054). There were no significant
differences in sex, Breslow thickness, stage, lymph node metastases, or distant metastases
when comparing SUM and AM and excluding in situ lesions (p= 0.936, 0.528, 0.745, 0.603,
and 0.989, respectively).
Table 3.
Differences in the clinic-pathologic features of subungual (n = 30) and acral (n = 59) inva-
sive melanomas.
No. (%) Subungual Acral p
Sex 0.936
Male 41 (46.1) 14 (46.7) 27 (45.8)
Female 48 (53.9) 16 (53.3) 32 (54.2)
Age (years) 0.054
≤63 35 (39.3) 16 (53.3) 19 (32.2)
>63 54 (30.7) 14 (46.7) 40 (67.8)
Tumor location 0.000
Upper 28 (31.5) 18 (60.0) 10 (16.9)
Lower 61 (68.5) 12 (40.0) 49 (83.1)
Breslow thickness 0.528
<1 mm 27 (30.3) 12 (40.0) 15 (25.4)
1.01–2.00 mm 15 (16.9) 4 (13.3) 11 (18.6)
2.01–4.00 mm 19 (21.3) 5 (16.7) 14 (23.7)
>4.00 mm 39 (31.5) 9 (30.0) 19 (32.2)
Lymph node metastasis
at the time of diagnosis 0.603
Absent 71 (79.8) 23 (76.7) 48 (81.4)
Present 18 (20.2) 7 (23.3) 11 (18.6)
Distant metastasis at
the time of diagnosis 0.989
Absent 86 (96.6) 29 (96.7) 57 (96.6)
Present 3 (3.4) 1 (3.3) 2 (3.4)
Stage group 0.745
I–II 70 (78.7) 23 (76.7) 47 (79.7)
III–IV 19 (21.3) 7 (23.3) 12 (20.3)
Cancers 2023,15, 4417 7 of 15
Table 3. Cont.
No. (%) Subungual Acral p
Immunotherapy 0.674
Not carried out 59 (66.3) 19 (63.3) 40 (67.8)
Carried out 30 (33.7) 11 (36.7) 19 (32.2)
Trauma 0.004
Absent 85 (95.5) 26 (86.7) 59 (100.0)
Present 4 (4.5) 4 (13.3) 0 (0.0)
Ulceration 0.714
Absent 54 (60.7) 19 (63.3) 35 (59.3)
Present 35 (39.3) 11 (36.7) 24 (40.7)
Loco-regional
recurrence 0.179
Absent 77 (86.5) 28 (93.3) 49 (83.1)
Present 12 (13.5) 2 (6.7) 10 (16.9)
Distant metastasis
during the follow-up 0.786
Absent 61 (68.5) 20 (66.7) 41 (69.5)
Present 28 (31.5) 10 (33.3) 18 (30.5)
3.3. Differences in Overall Survival of Patients with SUM or AM
Kaplan–Meier overall survival curves of patients with SUM and AM were stratified
according to stage and Breslow thickness (p= 0.004 and p< 0.001, respectively) (Supple-
mentary Figures S1 and S2). Patients with advanced-stage disease and greater invasion
depth had shorter overall survival. Univariate analysis of overall survival revealed that
patients with SUM had a better prognosis than patients with AM (p= 0.001; Figure 1a).
Patients with SUM had a better prognosis than patients with AM, including patients with
only invasive melanomas (p= 0.029) (Figure 1b). The mean survival time of SUM patients
was 6599 days (18 years), while the mean survival time of AM patients was 2744 days
(7.5 years). The 5-year survival rate was 87.1% for SUM patients and 48.7% for AM patients.
Cancers2023,15,xFORPEERREVIEW8of17
(a)(b)
Figure1.Kaplan–MeiercurvesshowingoverallsurvivalofpatientswithSUMandAM.(a)Allmel-
anomapatientswithSUMandAM,includinginsitumelanoma;(b)patientswithinvasivemela-
noma.
ACoxproportionalhazardsregressionmodelformultivariateanalysisofprognostic
factors,inwhichage(under63vs.over63),stage(0–IV),andSUMvs.AMwereentered
ascovariates,revealedthatSUMandstagewereindependentprognosticfactorsforthe
overallsurvivalofpatientswithSUMorAM(hazardratioforAM=2.936andp=0.016)
(Table4).MultivariateanalysisidentifiedSUMandlowerstageofdiseaseasprognostic
factorsforbeeroverallsurvival(p=0.016andp=0.038,respectively).ACoxproportional
hazardsregressionmodel,excludinginsitulesions,wasusedformultivariateanalysisof
prognosticfactors.ThismodelalsorevealedthatSUMandstagewereindependentprog-
nosticfactorsfortheoverallsurvivalofpatientswithSUMorAMwithinvasivelesions
(hazardratioforAM=2.462andp=0.040)(Table5).
Table4.Multivariateanalysisresultsforoverallsurvivalincludinginsitumelanomas.
MelanomaIncludingInSituLesionspHR95%CI
Subungualvs.Acral0.0162.9361.225–7.036
Age(under63yearsvs.over63years)0.2611.5290.730–3.205
Stage00.038
StageI0.4082.4740.289–21.177
StageII0.0756.5920.89–52.403
StageIII0.0399.3311.119–77.801
StageIV0.1677.3280.436–123.133
HR,hazardratio;CI,confidenceindex.
Table5.Multivariateanalysisresultsforoverallsurvivalwithinvasivemelanomas.
MelanomawithInvasiveLesionspHR95%CI
Subungualvs.Acral0.0402.4621.044–5.806
Age(under63yearsvs.over63years)0.2791.5040.718–3.151
StageI0.073
StageII0.0302.6281.099–6.282
StageIII0.0133.7231.325–10.459
StageIV0.3282.9090.342–24.716
HR,hazardratio;CI,confidenceindex.
3.4.DifferencesofSomaticMutationalSignaturesofPatientswithSUMorAM
Somaticalterationsin16patientswithprimaryandmetastaticSUMandsevenpa-
tientswithmetastaticAMwereanalyzedquantitativelybytheNGS-targetingof170
Figure 1.
Kaplan–Meier curves showing overall survival of patients with SUM and AM. (
a
) All
melanoma patients with SUM and AM, including in situ melanoma; (
b
) patients with inva-
sive melanoma.
A Cox proportional hazards regression model for multivariate analysis of prognostic
factors, in which age (under 63 vs. over 63), stage (0–IV), and SUM vs. AM were entered
as covariates, revealed that SUM and stage were independent prognostic factors for the
overall survival of patients with SUM or AM (hazard ratio for AM = 2.936 and p= 0.016)
(Table 4). Multivariate analysis identified SUM and lower stage of disease as prognostic
factors for better overall survival (p= 0.016 and p= 0.038, respectively). A Cox proportional
Cancers 2023,15, 4417 8 of 15
hazards regression model, excluding in situ lesions, was used for multivariate analysis
of prognostic factors. This model also revealed that SUM and stage were independent
prognostic factors for the overall survival of patients with SUM or AM with invasive lesions
(hazard ratio for AM = 2.462 and p= 0.040) (Table 5).
Table 4. Multivariate analysis results for overall survival including in situ melanomas.
Melanoma Including In Situ Lesions pHR 95% CI
Subungual vs. Acral 0.016 2.936 1.225–7.036
Age (under 63 years vs. over 63 years) 0.261 1.529 0.730–3.205
Stage 0 0.038
Stage I 0.408 2.474 0.289–21.177
Stage II 0.075 6.592 0.89–52.403
Stage III 0.039 9.331 1.119–77.801
Stage IV 0.167 7.328 0.436–123.133
HR, hazard ratio; CI, confidence index.
Table 5. Multivariate analysis results for overall survival with invasive melanomas.
Melanoma with Invasive Lesions pHR 95% CI
Subungual vs. Acral 0.040 2.462 1.044–5.806
Age (under 63 years vs. over 63 years) 0.279 1.504 0.718–3.151
Stage I 0.073
Stage II 0.030 2.628 1.099–6.282
Stage III 0.013 3.723 1.325–10.459
Stage IV 0.328 2.909 0.342–24.716
HR, hazard ratio; CI, confidence index.
3.4. Differences of Somatic Mutational Signatures of Patients with SUM or AM
Somatic alterations in 16 patients with primary and metastatic SUM and seven patients
with metastatic AM were analyzed quantitatively by the NGS-targeting of 170 cancer-
related genes according to molecular classification, origin of lesion, and stage of disease
(Figure 2). Molecular testing for common melanoma driver genes, including BRAF,NRAS,
KRAS,HRAS,NF1, and KIT, was available for this study.
Primary SUM most commonly presented with triple wild-type (negative for BRAF,
RAS,NF1) in 75% of cases, which were driven by GNAQ R183Q (58%) and KIT (25%)
mutations (Figure 2). The remaining primary SUM consisted of the RAS subtype (12.5%),
the BRAF subtype (6.3%), and the NF1 subtype (6.3%). Patients with primary SUM had
GNAQ R183Q (80%), KIT including K642E,V654A,N655K,D820Y (31.3%), NF1 S413
(6.3%), KRAS G12D (6.3%), NRAS G13D (6.3%), BRAF V600E (6.3%), PIK3CA E542K (6.3%),
CTNNB1 T41I (6.3%), and ATM A135 (6.3%) mutations (Figure 3a). SNVs (SUM4-SUM9)
were detected in patients with early-stage (in situ or T1a) primary SUM. The disease-
associated CNAs detected in the primary SUM were KIT (25%), CDK4 (25%), PDGFRA
(18.8%), MDM2 (18.8%), TERT (12.5%), and CCND2 (6.3%) amplifications (Figure 3b).
Somatic alterations of metastatic SUM and metastatic AM were compared. Metastatic
SUM most commonly presented with the KIT mutation (71.4%), followed by GNAQ R183Q
(28.6%), PIK3CA E542K (14.3%), BRAF V600E (14.3%), NRAS G13D (14.3%), and CTNNB1
T41I (14.3%) mutations (Figure 4a). Metastatic AM most commonly presented with BRAF,
including V600E and K601E (28.6%) followed by NRAS Q61K (14.3%) mutations (Figure 4a).
The disease-associated CNAs detected in the patients with metastatic SUM were KIT
(42.3%), TERT (42.3%), PDGFRA (28.6%), CDK4 (28.6%), MDM2 (28.6%) amplifications,
and CDKN2A (28.6%) and CDKN2B (33.3%) deletions (Figure 4b). The common disease-
associated CNAs detected in the patients with metastatic AM were CDKN2A (57.1%)
deletion, BRAF (42.9%) and TERT (42.9%) amplification, CDKN2B (28.6%) deletion, and
Cancers 2023,15, 4417 9 of 15
CDK6 (28.6%) and MYC (28.6%) amplification (Figure 4b). One metastatic AM patient
harbored an MKRN1-BRAF translocation (14.2%).
Cancers2023,15,xFORPEERREVIEW9of17
cancer-relatedgenesaccordingtomolecularclassification,originoflesion,andstageof
disease(Figure2).Moleculartestingforcommonmelanomadrivergenes,including
BRAF,NRAS,KRAS,HRAS,NF1,andKIT,wasavailableforthisstudy.
Figure2.Somaticmutationalsignaturesofsubungualandacralmelanomas.*,aminoacidchanges
oftheKITgene.Redbar,singlenucleotidevariation.Greenbar,copynumberamplification;Blue
bar,copynumberdeletion.Yellowbar,Translocation.
PrimarySUMmostcommonlypresentedwithtriplewild-type(negativeforBRAF,
RAS,NF1)in75%ofcases,whichweredrivenbyGNAQR183Q(58%)andKIT(25%)mu-
tations(Figure2).TheremainingprimarySUMconsistedoftheRASsubtype(12.5%),the
BRAFsubtype(6.3%),andtheNF1subtype(6.3%).PatientswithprimarySUMhadGNAQ
R183Q(80%),KITincludingK642E,V654A,N655K,D820Y(31.3%),NF1S413(6.3%),KRAS
G12D(6.3%),NRASG13D(6.3%),BRAFV600E(6.3%),PIK3CAE542K(6.3%),CTNNB1
T41I(6.3%),andATMA135(6.3%)mutations(Figure3a).SNVs(SUM4-SUM9)werede-
tectedinpatientswithearly-stage(insituorT1a)primarySUM.Thedisease-associated
CNAsdetectedintheprimarySUMwereKIT(25%),CDK4(25%),PDGFRA(18.8%),
MDM2(18.8%),TERT(12.5%),andCCND2(6.3%)amplifications(Figure3b).
Figure3.Frequencyofalterationsinmutatedgenesofpatientsofsubungualmelanoma(SUM):(a)
single-nucleotidepolymorphism(SNP)frequenciesand(b)copynumberalteration(CNA)frequen-
cies.
Figure 2.
Somatic mutational signatures of subungual and acral melanomas. *, amino acid changes
of the KIT gene. Red bar, single nucleotide variation. Green bar, copy number amplification; Blue bar,
copy number deletion. Yellow bar, Translocation.
Cancers2023,15,xFORPEERREVIEW9of17
cancer-relatedgenesaccordingtomolecularclassification,originoflesion,andstageof
disease(Figure2).Moleculartestingforcommonmelanomadrivergenes,including
BRAF,NRAS,KRAS,HRAS,NF1,andKIT,wasavailableforthisstudy.
Figure2.Somaticmutationalsignaturesofsubungualandacralmelanomas.*,aminoacidchanges
oftheKITgene.Redbar,singlenucleotidevariation.Greenbar,copynumberamplification;Blue
bar,copynumberdeletion.Yellowbar,Translocation.
PrimarySUMmostcommonlypresentedwithtriplewild-type(negativeforBRAF,
RAS,NF1)in75%ofcases,whichweredrivenbyGNAQR183Q(58%)andKIT(25%)mu-
tations(Figure2).TheremainingprimarySUMconsistedoftheRASsubtype(12.5%),the
BRAFsubtype(6.3%),andtheNF1subtype(6.3%).PatientswithprimarySUMhadGNAQ
R183Q(80%),KITincludingK642E,V654A,N655K,D820Y(31.3%),NF1S413(6.3%),KRAS
G12D(6.3%),NRASG13D(6.3%),BRAFV600E(6.3%),PIK3CAE542K(6.3%),CTNNB1
T41I(6.3%),andATMA135(6.3%)mutations(Figure3a).SNVs(SUM4-SUM9)werede-
tectedinpatientswithearly-stage(insituorT1a)primarySUM.Thedisease-associated
CNAsdetectedintheprimarySUMwereKIT(25%),CDK4(25%),PDGFRA(18.8%),
MDM2(18.8%),TERT(12.5%),andCCND2(6.3%)amplifications(Figure3b).
Figure3.Frequencyofalterationsinmutatedgenesofpatientsofsubungualmelanoma(SUM):(a)
single-nucleotidepolymorphism(SNP)frequenciesand(b)copynumberalteration(CNA)frequen-
cies.
Figure 3.
Frequency of alterations in mutated genes of patients of subungual melanoma (SUM): (
a
) single-
nucleotide polymorphism (SNP) frequencies and (b) copy number alteration (CNA) frequencies.
Cancers2023,15,xFORPEERREVIEW10of17
SomaticalterationsofmetastaticSUMandmetastaticAMwerecompared.Metastatic
SUMmostcommonlypresentedwiththeKITmutation(71.4%),followedbyGNAQ
R183Q(28.6%),PIK3CAE542K(14.3%),BRAFV600E(14.3%),NRASG13D(14.3%),and
CTNNB1T41I(14.3%)mutations(Figure4a).MetastaticAMmostcommonlypresented
withBRAF,includingV600EandK601E(28.6%)followedbyNRASQ61K(14.3%)muta-
tions(Figure4a).Thedisease-associatedCNAsdetectedinthepatientswithmetastatic
SUMwereKIT(42.3%),TERT(42.3%),PDGFRA(28.6%),CDK4(28.6%),MDM2(28.6%)
amplifications,andCDKN2A(28.6%)andCDKN2B(33.3%)deletions(Figure4b).The
commondisease-associatedCNAsdetectedinthepatientswithmetastaticAMwere
CDKN2A(57.1%)deletion,BRAF(42.9%)andTERT(42.9%)amplification,CDKN2B
(28.6%)deletion,andCDK6(28.6%)andMYC(28.6%)amplification(Figure4b).Onemet-
astaticAMpatientharboredanMKRN1‐BRAFtranslocation(14.2%).
Figure4.Changesinsomaticmutationalterationsofprimaryandmetastaticsubungualandacral
melanomas:(a)single-nucleotidepolymorphism(SNP)frequenciesand(b)copynumberalteration
(CNA)frequenciesofmetastaticmelanomas.
3.5.ComparisonofSomaticMutationsofPrimaryandMetastaticMelanomasofSUM
andAM
TocomparethemolecularprofilesofpairedprimaryandmetastaticSUMandAM
tumors,weexaminedsevenpatientswithSUMandfivepatientswithAM(Figure5).All
metastatictumorsretainedallofthegeneticSNVsidentifiedintheprimarytumors.Four
outofsevenpatients(57%)withSUMandoneoutoffivepatients(20%)withAMhad
identicalmutationalsignaturesintheprimaryandmetastatictumors.Inthemetastatic
lesions,tumorsgainedadditionalCNAs.PatientswithSUMgainedCDKN2A(2/7pa-
tients;28.6%)andCDKN2B(2/7patients;28.6%)deletionsandBRAF(1/7;14.3%),TERT
(1/7;14.3%),andNOTCH2(1/7;14.3%)amplifications.Metastatictumorsfrompatients
withAMgainedCDKN2A(2/5;40%)andPTEN(1/5;20%)deletionsandBRAF(2/5;40%),
TERT(2/5;40%),CDK6(1/5;20%),MYC(1/5;20%),CCND1(1/5;20%),FGF19(1/5;20%),
FGF3(1/5;20%),andMDM2(1/5;20%)amplifications.
Figure 4.
Changes in somatic mutation alterations of primary and metastatic subungual and acral
melanomas: (
a
) single-nucleotide polymorphism (SNP) frequencies and (
b
) copy number alteration
(CNA) frequencies of metastatic melanomas.
Cancers 2023,15, 4417 10 of 15
3.5. Comparison of Somatic Mutations of Primary and Metastatic Melanomas of SUM and AM
To compare the molecular profiles of paired primary and metastatic SUM and AM
tumors, we examined seven patients with SUM and five patients with AM (Figure 5). All
metastatic tumors retained all of the genetic SNVs identified in the primary tumors. Four
out of seven patients (57%) with SUM and one out of five patients (20%) with AM had
identical mutational signatures in the primary and metastatic tumors. In the metastatic
lesions, tumors gained additional CNAs. Patients with SUM gained CDKN2A (2/7 patients;
28.6%) and CDKN2B (2/7 patients; 28.6%) deletions and BRAF (1/7; 14.3%), TERT (1/7;
14.3%), and NOTCH2 (1/7; 14.3%) amplifications. Metastatic tumors from patients with
AM gained CDKN2A (2/5; 40%) and PTEN (1/5; 20%) deletions and BRAF (2/5; 40%),
TERT (2/5; 40%), CDK6 (1/5; 20%), MYC (1/5; 20%), CCND1 (1/5; 20%), FGF19 (1/5; 20%),
FGF3 (1/5; 20%), and MDM2 (1/5; 20%) amplifications.
Cancers2023,15,xFORPEERREVIEW11of17
Figure5.Somaticmutationalalterationcomparisonofprimaryandmetastatictumorsofsubungual
andacralmelanoma.Graybar,nochangeofthemutation.Yellowbar,acquisitionofcopynumber
alterationinthemetastatictumor.
WevalidatedcasesofSUMandAM(SUM13andAM2;Figure4)withdoublelesions
ofmetastaticmelanomas;onecase(AM2)gainedCNAsinthesecondmetastatictumor
andtheother(SUM13)hadthesamemutationalsignatureinthefirstandsecondmeta-
statictumor.
4.Discussion
TheclinicalcharacteristicsofourpatientswithSUMwerecomparedwiththeclinical
characteristicsofpatientsreportedinpreviousstudies(Table6).Thepreviousstudies
showeddifferentgenderpredominance,dependingonthepatients’raceandlocation[14–
18].Themale-to-femaleratioinourstudywas0.91,andslightlymorewomenthanmen
hadSUM.ThemeanageofourSUMpatientswas56years,whichwassimilartothat
reportedintheliterature(47–66years)[8,18–20].MostpreviousstudiesreportedSUM
locatedonthefirstfingernail[4,7,16–19,21].WefoundthatSUMwasmostcommoninthe
nailsoftheupperextremity(69%).ThediseasestageanddepthofinvasionofSUMvaried,
withmanystudiesreportingstageII(38.7%)[21],stageIII(52%)[22],ClarklevelIV(53.4%
and70%)[7,20],andClarklevelIV/V(79%)asthemostcommonstages[23].Leeetal.
reportedthatthemostcommonstagewasstage0(insitu)in63.2%ofSUMpatients,and
theirstudyexaminedmostlyCaucasianandAfrican-Americanpatients[8].Here,we
foundthatthemostcommonstagewasstage0(insitu)in28.6%oftheSUMpatientsand
stageIIin28.6%oftheSUMpatients.
Tab l e6.SummaryofclinicalandmutationalprofilesofSUMintheliterature.
ClinicalandMolecularProfilesSubungualMelanoma
SexMalepredominance[4,7,14,15,17,21,24]
Femalepredominance[8,14–16,25].
Meanage(years)47–66years[4,7,8,14–18,21].
ThemostcommontumorlocationFingernail(17–63%)[4,7,14,16–19,21,25]
Toenail(26.3%,68%,and78%)[15,24]
ThemostcommonClarklevelClarklevelIV(37%,53%,and70%)
[7,15,18,21]
ThemostcommonBreslowthickness
≤1mm(63.2%)[8]
1.01–4mm(34–50%)[7,18,21,24]
>4mm(31%,34.9%,50%)[14,20,25]
Themostcommonstagegroup0(insitu)(63.2%)[8].
I(83%)[17]
Figure 5.
Somatic mutational alteration comparison of primary and metastatic tumors of subungual
and acral melanoma. Gray bar, no change of the mutation. Yellow bar, acquisition of copy number
alteration in the metastatic tumor.
We validated cases of SUM and AM (SUM13 and AM2; Figure 4) with double lesions of
metastatic melanomas; one case (AM2) gained CNAs in the second metastatic tumor and the
other (SUM13) had the same mutational signature in the first and second metastatic tumor.
4. Discussion
The clinical characteristics of our patients with SUM were compared with the clini-
cal characteristics of patients reported in previous studies (Table 6). The previous stud-
ies showed different gender predominance, depending on the patients’ race and loca-
tion
[14–18]
. The male-to-female ratio in our study was 0.91, and slightly more women
than men had SUM. The mean age of our SUM patients was 56 years, which was similar to
that reported in the literature (47–66 years) [
8
,
18
–
20
]. Most previous studies reported SUM
located on the first fingernail [
4
,
7
,
16
–
19
,
21
]. We found that SUM was most common in the
nails of the upper extremity (69%). The disease stage and depth of invasion of SUM varied,
with many studies reporting stage II (38.7%) [
21
], stage III (52%) [
22
], Clark level IV (53.4%
and 70%) [
7
,
20
], and Clark level IV/V (79%) as the most common stages [
23
].
Lee et al.
reported that the most common stage was stage 0 (in situ) in 63.2% of SUM patients, and
their study examined mostly Caucasian and African-American patients [
8
]. Here, we found
that the most common stage was stage 0 (in situ) in 28.6% of the SUM patients and stage II
in 28.6% of the SUM patients.
Cancers 2023,15, 4417 11 of 15
Table 6. Summary of clinical and mutational profiles of SUM in the literature.
Clinical and Molecular Profiles Subungual Melanoma
Sex Male predominance [4,7,14,15,17,21,24]
Female predominance [8,14–16,25].
Mean age (years) 47–66 years [4,7,8,14–18,21].
The most common tumor location Fingernail (17–63%) [4,7,14,16–19,21,25]
Toenail (26.3%, 68%, and 78%) [15,24]
The most common Clark level
Clark level IV (37%, 53%, and 70%) [
7
,
15
,
18
,
21
]
The most common Breslow thickness
≤1 mm (63.2%) [8]
1.01–4 mm (34–50%) [7,18,21,24]
>4 mm (31%, 34.9%, 50%) [14,20,25]
The most common stage group
0 (in situ) (63.2%) [8].
I (83%) [17]
II (32.6–53.7%) [14,15,20]
III (32% and 52%) [21,24]
Lymph node metastasis at the time of diagnosis
9–62.3% [15–18,21,24]
Distant metastasis at the time of diagnosis 9.3% and 42.6% [18,20]
Trauma 15.8% and 48% [4,8]
Ulceration 47–76% [7,14–17,20,21,24]
5-year disease free survival 40% and 57% [7,18]
5-year survival 74–97% [15,17,18,26]
Overall mortality 17%, 31%, and 46% [17,18,21]
BRAF V600E mutation 0–40% [4,5,14,16,27]
NRAS mutation 0–31% [4,14,16,27]
KRAS mutation 6.5% and 11% [4,27]
NF1 mutation 0–50% [4,27]
C-KIT mutation 11.1%, 13%, and 16% [4,14,16,27]
GNAQ mutation 0–25% [27]
Melanoma of the subungual and palmoplantar areas is categorized as AM or acral
lentiginous melanoma. SUM is a rare type of melanoma in Caucasians, while SUM and
AM are more common subtypes in Asians. SUM is a subtype of AM, which is both
aggressive and one of the most common types of melanoma in Asians [
3
]. In Asian patients,
SUM accounts for 10–17.5% of cutaneous melanoma cases [
26
,
28
] and 26–30% of AM
cases [
21
,
29
]. SUM accounted for 14% of melanoma cases and 28% of AM cases in our study
(Supplementary Table S3). Several papers have reported that SUM has pathologic features
that are similar to those of AM, which is in contrast to other variants of melanoma, including
the lentigo maligna type, the superficial spreading type, and the nodular type [
30
,
31
]. SUM
and AM have histologic similarities with respect to radial growth patterns, lower local
growth rates, high content of spindle cells, and advanced stages [21,30,31].
Despite these histologic similarities, different clinical features between SUM and AM
have been reported. Patients with SUM were younger than those with AM, a finding
consistent with our own findings [
4
,
7
]. We found that SUM develops more frequently on
the hands, while AM develops more frequently on the foot. Patients with SUM reported a
higher incidence of previous trauma to the lesions than those patients with AM. A previous
study reported that ulcerations were more common in patients with SUM than they were in
patients with AM, although other studies (including ours) showed no difference between
SUM and AM in that regard [
4
,
7
,
20
]. Previous studies reported no difference between SUM
and AM in the depths of Breslow thickness, the pathologic stages, or the Clark levels [
4
,
7
,
21
].
Holman et al. showed that patients with SUM had an increased frequency of metastases,
but took longer to develop distant metastasis [
4
]. In our study, we found that the depth of
tumor invasion was shallower and the tumor stage was earlier in patients with SUM than
in patients with AM. Loco-regional recurrence was less common in patients with SUM than
in patients with AM, due to including in situ lesions of SUM. The stages and the depths of
SUM and AM did not differ when in situ lesions were excluded.
Cancers 2023,15, 4417 12 of 15
Patients with AM are considered to have a grave prognosis and to develop metas-
tases more quickly than those with other subtypes of melanoma. Mejbel et al. reported
that patients with SUM have a higher risk of death, but subungual location was not an
independent prognostic factor [
7
]. Holman et al. and Jung et al. reported no significant
difference in the survival of patients with AM or SUM [
4
,
20
]. Here, we found that the 5-year
survival rates for patients with SUM was 87.1%. Subungual rather than acral location was
an independent prognostic factor for better overall survival. We hypothesized that the
poor prognosis of patients with SUM, as reported in prior studies, might be due to late
presentation or late implementation of clinical management. Usually, SUM presents as
a brown-black discoloration of the nail bed, and it is commonly misdiagnosed as striate
melanonychia and onychomycosis. Prior studies commonly reported patients with SUM
at an advanced stage [
20
–
23
]. SUM tumors were often ulcerated and deep, resulting in
5-year survival rates of approximately 40% [
19
,
20
]. Mejbel et al. enrolled mostly advanced
staged (stage IV in 70%) patients with SUM and reported 5-year overall survival rates of
40% [
7
]. In the present study, most patients were diagnosed early, as stage 0 or stage II
(26.2%), and multivariate analysis adjusted for stage and age showed that patients with
SUM had better overall survival than patients with AM. SUM patients, excluding in situ
cases, also showed better overall survival than patients with AM. Lee et al. enrolled 63.2%
of patients with in situ melanoma, and all of those patients with SUM survived during the
5-year follow-up [
8
]. They also found that early diagnosis was a good prognostic feature
for SUM [8].
Recently, melanomas were classified into different subtypes according to their etiologi-
cal relationship to sun exposure, mutational signatures, anatomic sites, and epidemiology.
SUM and AM showed different molecular characteristics related to cumulative solar dam-
age [
4
,
5
]. SUM had a mutational signature related to UVR, whereas AM appeared to have
little or no relation to UVR [
5
,
6
]. Different molecular pathogenesis to UVR may affect
clinical and molecular characteristics of SUM that are distinct from those of AM. The
previous somatic mutations of SUM vary the GNAQ (0–25%), KIT (0–50%), NF1 (0–50%),
BRAF (0–43%), and NRAS (0–31%) mutations that have been reported [
4
,
5
,
18
,
25
,
27
,
32
–
40
]
(Table 6). We found that most patients with SUM had triple wild-type disease driven by
GNAQ R183 and KIT mutations, whereas most patients with AM showed BRAF (including
V600 and K601) and RAS (NRAS Q61,NRAS G13, and KRAS G12) molecular types. Deletion
of the cell cycle pathway gene CDKN2A/B (p16) occurred more frequently in patients with
AM than in patients with SUM. Patients with SUM had more SNVs, but CNAs were more
common in patients with AM. Haugh et al. described the higher frequency of CNAs of
CDK4 and CCND1, and few BRAF mutations with SUM [
34
]. Complex gene rearrangements
in melanomas may be potential molecular therapeutic targets in melanoma patients [
5
].
The inconstant mutational profiles of SUM in previous studies require further investigation.
This is the first study to validate the molecular characteristics of matched primary and
corresponding metastatic tumors from patients with SUM and to compare them with those
of patients with AM. All of the metastatic tumors retained all genetic SNVs found in the
primary tumors, and half of the patients with SUM and one-fifth of the patients with AM
showed identical mutational signatures of primary and metastatic tumors. Interestingly,
metastatic tumors gained additional CNAs, but not SNVs, and the number of CNAs
increased in metastatic tumors. The metastatic tumors in AM showed more frequent
acquisition of CNVs, but the mutational signatures of SUM and AM were similar. CDKN2A
and CKDN2B deletions and BRAF and TERT amplifications were common in the metastatic
tumors of SUM and AM.
Turajlic et al. detected a wide ranged genetic heterogeneity (11–84%) in both the
primary and metastatic tumors of AM [
41
]. Manca et al. used target panel NGS sequencing
to show a high level of concordance between the mutational patterns of primary and
metastatic cutaneous melanoma, reporting that the consistency of pathogenic mutations
was 76% [
42
]. Herein, our panel NGS sequencing revealed mutational consistency in 57%
of SUM primary and matched metastatic tumors and 25% of AM primary and matched
Cancers 2023,15, 4417 13 of 15
metastatic tumors. Sanborn et al. conducted whole-exome sequencing of cutaneous
melanomas and reported that genetically distinct cell populations in the primary tumor
metastasized to different anatomic sites in 6 out of 8 cases, indicating a late-evolving trait
of metastases [
43
]. Discrepancies between these prior studies and our study may be due
to (i) different NGS platforms and interpretation of mutations, (ii) validation of different
subtypes of melanoma, and (iii) studies involving different races. Turajlic et al. described
highly similar levels of SNVs and CNAs in primary and metastatic tumors, and they
suggested that metastatic tumor clones stem from non-modal sub-clones of the primary
melanoma that emerged at a late stage of development of the primary melanoma, or that
metastatic clones harbored specific mutations in addition to the mutations found in the
modal population of the primary melanoma [41].
This study had several limitations, including the small sample size, the retrospective
design, and the inclusion of patients from a single institution. The number of tissue samples
enrolled were limited, due to a high failure rate of sequencing (more than 60%). Melanin
pigment, decalcification during the sample processing from nails, and scattered tumor cells
in the early lesion caused poor DNA quality. Patients with AM were only selected if they
had both primary and metastatic tumor samples. The molecular profiles of primary SUM
could not be compared equally with the results of AM, due to selection bias. However, our
data highlight the distinct clinicopathologic features of SUM, new data regarding overall
survival, and molecular data from Asian patients with SUM. Early detection of SUM results
in a good prognosis for patients with SUM. Therefore, we propose that clinical management
of SUM melanoma should be revalidated, based on race. A deeper understanding of the
molecular and immunologic characteristics of SUM is required to select appropriate clinical
treatment strategies, including targeted molecular agents.
5. Conclusions
Herein, we reported differences in the clinicopathologic and mutation profiles of SUM
and AM in Asian patients. SUM was related to favorable clinical factors and showed
better overall survival. The molecular profiles of SUM (mostly triple wild-type driven by
the GNAQ R183 and KIT mutations) were different from those of AM. SNVs were more
common in metastatic lesions of SUM, whereas CNAs were more common in metastatic
lesions of AM. Patients with SUM may require different therapies, depending on the
distinct anatomical locations and molecular characteristics of the tumors. We suggest that
SUM should not be categorized along with AMs. Rather, it should be considered as a
separate entity.
Supplementary Materials:
The following supporting information can be downloaded at: https:
//www.mdpi.com/article/10.3390/cancers15174417/s1, Figure S1: Kaplan–Meier curves showing
overall survival of patients with SUM and AM stratified according to the stages. (left) All melanoma
patients with SUM and AM, including in situ melanoma; (right) patients with invasive melanoma;
Figure S2: Kaplan–Meier curves showing overall survival of patients with SUM and AM stratified
according to the Breslow thickness. (left) All melanoma patients with SUM and AM, including in situ
melanoma; (right) patients with invasive melanoma; Table S1: Demographic data of 42 patients with
subgual melanoma during 15 years; Table S2: Gene lists for Oncomine Comprehensive Assay version
3 (n = 170); Table S3: Melanoma patients enrolled in pathology archives in a single institute (CNUH)
from 200 to 2022 (15 years).
Author Contributions:
Resources and data curation, M.-K.Y. and G.-E.B.; conceptualization and
validation, M.-K.Y. and S.-Y.A.; formal analysis, M.-K.Y.; funding, M.-K.Y.; supervision, writing-
original draft, writing—review and editing, S.-Y.P. and M.-K.Y. All authors have read and agreed to
the published version of the manuscript.
Funding:
M.-K.Y. was supported by a research fund of the Chungnam National University, Korea Health
Technology R&D Project, through the Korea Health Industry Development Institute (KHIDI), funded by
the Ministry of Health & Welfare, Republic of Korea (HR20C0025), and by a National Research Foundation
of Korea (NRF) grant funded by the Korean government (MSIT) (RS2023-00210264).
Cancers 2023,15, 4417 14 of 15
Institutional Review Board Statement:
This retrospective study was approved by the Chungnam
National University Hospital institutional review board (IRB file no. CNUH 2020-09-015), which
waived the requirement for informed consent.
Informed Consent Statement:
A waiver of informed consent was approved for this research, in
CNUH IRB 2020-09-015.
Data Availability Statement:
The raw data were generated at CNUH and derived data supporting
the findings of this study are available from the corresponding author on request.
Conflicts of Interest: The authors declare that they have no conflict of interest.
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