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Merits of the PMiT (Papillary
Microtumor) Terminology in the
Definition of a Subset of Incidental
Papillary Microcarcinomas of the Thyroid
Sofia Asioli, MD, Chiara Odasso, MD, Luigia Macrì, MD,
Nicola Palestini, MD, and Gianni Bussolati, MD, FRCPath
The incidence of thyroid cancer, particularly the
papillary forms, has been increasing sharply for many
years in Western countries. Recently, Colonna et al2
published a study on changes in the incidence of
both papillary and follicular thyroid cancers and the
effect of tumor size from data taken from 6 cancer
registries in France (1983-2000). They found that
the increase in papillary carcinomas was high for
both sexes; in particular, the study showed that the
sharpest increase with a yearly progression of more
than 12% was observed for carcinomas smaller than
10 mm.2A change in the distribution of the size of
papillary carcinomas has also been described in the
United States, where the estimated proportion of
microcarcinomas within papillary thyroid carcinomas
(PTCs) was 27% in 1996.3In Switzerland, an
increase was observed in thyroid microcarcinomas,
mainly of the papillary type, which rose from 17%
during the 1970 to 1979 period to 24% during the
1990 to 1998 period.4In Italy, Trimboli et al5
recently evaluated the temporal trend in tumor size,
Introduction
According to the latest World Health Organization
(WHO) definition, published in 2004, papillary thy-
roid microcarcinoma (PTMC) is defined as a papillary
carcinoma, often not detectable in clinical examina-
tion, that is found incidentally (ie, after thyroidectomy
performed for other indications or during ultrasound
examination) and measures ≤1 cm in diameter.1
An exponential increase in the detection of papillary
thyroid microcarcinomas (PTMCs) has been observed
in recent times, possibly because of recent improve-
ments in the management of thyroid lesions and exten-
sive histological examination. However, no definitive
treatment guideline has been developed for PTMC,
resulting in patients undergoing overtreatment. In
2003, the term papillary microtumor of the thyroid
(PMiT) was proposed for small (≤1 cm) intrathyroidal
tumors with excellent prognostic prospects along with
strict definition criteria. Since then, the term PMiT
has been adopted by clinicians and surgeons. In this
article, the authors report a series of 50 consecutive
cases of PMiT collected and treated at the University
Hospital of Turin, Italy. From the authors’ experience,
this terminology, which demarks a subset of PTMC,
should be widely adopted as it is biologically sound,
well accepted by both clinicians and patients,
decreases the danger of overtreatment, minimizes the
psychological anxiety engendered by a diagnosis of car-
cinoma, and maintains the patient’s eligibility for
health insurance.
Keywords: PMiT; papillary; microcarcinoma; thyroid
From the Departments of Biomedical Sciences and Oncology
(SA, LM, GB) and Surgery (CO, NP), University of Turin,
Turin, Italy.
This study was supported by grants from AIRC (Associazione
Italiana per la Ricerca sul Cancro), MIUR, Piedmont Region,
Compagnia di San Paolo “Special Project Oncology” and the
Fondazione Internazionale di Ricerca in Medicina Sperimentale
(FIRMS), Turin, Italy.
Address correspondence to: Sofia Asioli, MD, Department of
Biomedical Sciences and Human Oncology, Molinette Hospital,
University of Turin, Via Santena 7, 10126 Turin, Italy; e-mail:
sofia.asioli@unito.it.
International Journal of
Surgical Pathology
Volume XX Number X
Month XXXX xx-xx
© 2008 Sage Publications
10.1177/1066896908321181
http://ijsp.sagepub.com
hosted at
http://online.sagepub.com
2International Journal of Surgical Pathology / Vol. XX, No. X, Month XXXX
age at diagnosis, and histology in a retrospective
analysis of 500 thyroid cancers diagnosed over 20
years at the Thyroid Clinic of the University of Rome
“La Sapienza.” They found that the size of the PTC
decreased from 28 ±1.2 to 14 ±0.8 mm in the last
decade. Moreover, a significant increase of PTMC
rate, from 7.3% to 36.4%, was also observed.5This
exponential increase in the detection of PTCMs
could possibly be explained by recent improvements
in the management of thyroid lesions as well as
extensive histological examination of thyroid lesions.
From a pathology point of view, PTMCs are
small (≤1 cm) papillary carcinomas that share archi-
tectural, cytological, immunohistochemical, and
clinical features with their larger counterparts. The
clinical behavior of PTCM is usually indolent.6
Sometimes PTMCs present as “occult” carci-
noma and may have a clinical behavior, presenting
with regional lymph node metastases or, more rarely,
distant metastases.7-11 In an earlier study,12 PTMCs
presenting as a “histological surprise” were free of dis-
ease during a follow-up of 3 to 23 years, with a mean
of 6.4 years, and there was no single instance of dis-
tant metastasis.
However, no definitive treatment guideline has
yet been developed to indicate how best to treat and
manage these small tumors. The confusion sur-
rounding the definition and the treatment of PTMC
has been made plainly evident in various scientific
articles on the subject.13-20 The guidelines for differ-
entiated thyroid carcinoma recently published by
the American Thyroid Association21 and the
European Thyroid Association22 agree that in cases
of PTMC therapy should be adapted to the method
of discovery and to favorable prognostic criteria (ie,
unifocal lesion, classical histological subtype, no
extension beyond the thyroid capsule, no lymph
node metastasis, and normal contralateral lobe).
The existence of a subset of incidental papillary
microcarcinomas of the thyroid, defined as unifocal
small (≤1 cm) lesion with no extension beyond the thy-
roid capsule and without lymph node metastasis with
benign clinical course, is indisputable, and this subset
of PTMC could be designated from clinical and
histopathological points of view as a “minimal risk
group” of thyroid lesions, keeping in mind that we are
dealing with patients who have a normal life expectancy
and to whom we have to guarantee a very good quality
of life.
A panel of 4 thyroid pathologists, involved in a
consensus meeting that took place in Porto, March
3-5, 2003, during the 12th Annual Cancer Meeting,
aimed at developing uniform diagnostic criteria for
PTMC carcinomas and proposing a new term for a
subset of PTCM. Indeed, the panel renamed such a
subset of PTMC as “papillary microtumor” (PMiT).
Diagnosis of PMiT has to be based on the following
criteria: (a) size (≤1 cm); (b) absence of metastases
at presentation; (c) adult patients only; (d) unifocal
or multifocal lesions (2 or more lesions are detected
to be ≤1 cm); (e) exclusion of features indicative of
invasion of the thyroid capsule, blood vessel perme-
ation, or tall cells features; (f) PMiT could occur
within a benign lesion; and (g) PMiT could be occa-
sionally detected preoperatively at ultrasound exam-
ination, computed tomography, or magnetic resonance
imaging23 (Table 1).
The term PMiT was chosen because it indicates
that the lesion is of a small size, is a neoplastic
process belonging to the papillary family neoplasm,
and is not necessarily malignant. We are not aware
of other endocrine pathology centers having adopted
this terminology. However, since 2003, we have
adopted the Porto proposal criteria for PMiT, in
agreement with clinicians and surgeons. We report
our experience on a series of 50 consecutive cases
designated as PMiT (during the period from March
2003 to August 2007) and treated at our hospital.
Materials and Methods
Clinical Data
Cases were obtained from the files of all thyroid
specimens (1407 cases) analyzed at the Department
of Biomedical Sciences and Human Oncology,
University of Turin, during the period from March
2003 to August 2007. The lesions were diagnosed
as benign thyroid diseases (ie, goiters, thyroid
Table 1. Diagnostic Criteria of Papillary Microtumor
According to the Porto Proposal
Age ≥19 years
Size ≤1 cm
Metastases at presentation No
Number of lesions One or more (<1 cm when take
together)
Capsule invasion No
Vascular invasion No
Tall cells features No
Benign lesions Yes
Radiological images Detectable (≤1 cm)
PMiT (Papillary Microtumor): A Subset of PTMC / Asioli et al 3
autoimmune diseases, cystic lesions, follicular ade-
nomas) in 1052 cases (74.8%) and as malignant
thyroid lesions (ie, primary thyroid carcinomas, pri-
mary thyroid lymphoma, metastatic lesions) in 355
cases (25.2%). Among these cases, 273 (273/355,
76.9%) were diagnosed as papillary thyroid neoplasm,
specifically, 154 (154/273, 56.4%) PTC (>1 cm), 10
(10/273, 3.7%) “occult” PTMC (≤1 cm), 59
(59/273, 21.6%) “incidental” PTMC (≤1 cm), and
50 (50/273, 18.3%) PMiT (Figure 1).
In this article, we report a series of 50 consecutive
cases designated as PMiT, according to predefined cri-
teria. All patients were white individuals who were
treated at the same surgical init (ie, the Department of
Surgery at the Molinette Hospital, University of Turin).
Thirty-nine of the 50 cases designated as PMiT
(78%) were females and 11 (22%) were males, with
ages ranging from 38 to 77 years (median age of 55.1
years) and from 30 to 79 years (median age of 58.3
years), respectively, at the time of presentation.
Patients presented with goiter (40/50 cases, 80%),
solitary nodule (9/50 cases, 18%), and chronic lym-
phatic thyroditis (1/50 cases, 2%) at clinical observa-
tion. The hormonal status of the patients at
presentation was hypothyroidism (1/50 patient, 2%),
hyperthyroidism (7/50 patients, 14%), or euthy-
rodism (40/50 patients, 80%); 2 patients showed pri-
mary hyperparathyroidism (2/50 patients, 4%).
All patients underwent surgery, with 47 patients
undergoing total thyroidectomy without lymphade-
nectomy (47/50 cases, 94%) and 3 patients being
subjected to lobectomy (3/50 cases, 6%). Complica-
tions associated with surgery were permanent
hypoparathyroidism in 1 patient also submitted to
subtotal parathyroidectomy for primary hyperparathy-
roidism (2%), transient hypoparathyroidism in 2 cases
(4%), and temporary hypomobility of 1 vocal cord in 1
patient (1/50, 2%). No further treatment, including
radioiodine treatment, was provided. Follow-up data
were available for all patients (see below).
Histology
Tissues were fixed in buffered formalin and routinely
embedded in paraffin, and slides were stained with
hematoxylin and eosin. Two pathologists (GB and SA)
reviewed all cases according to the WHO classifica-
tion and the Porto proposal criteria (see above).1,23
Results
Papillary Microtumor Cases
Fifty out of the 119 cases of small papillary thyroid
lesions met the Porto proposal criteria. In particular, all
patients were adults (>19 years) without metastases at
presentation, and we excluded, from this category,
those cases (69/119 cases of PTMC) wherein the
tumor had features indicative of a potential for an
aggressive behavior (ie, invasion of the thyroid capsule,
blood vessel permeation, or tall cells features). We
identified a single focus of papillary microtumor in
43/50 cases and 2 lesions, less than 1 cm in diameter
when taken together, in 7/50 cases that were contained
within the thyroid gland and were found accidentally at
thyroidectomy done for some reason other than PMiT.
The prevalence of PMiT diagnosis was 3.6%
(50/1407 cases) in all the thyroid specimens ana-
lyzed at the Department of Biomedical Sciences and
Human Oncology, University of Turin, during the
period from March 2003 to August 2007. Indeed,
we found the following annual prevalences of PMiT:
0.6% (1/162) during the period from March to
December 2003, 5.2% (16/305) during the period
from January to December 2004, 5.9% (22/370)
during the period from January to December 2005,
2.5% (8/326) during the period from January to
December 2006, and 1.2% (3/244) during the
period from January to August 2007 (Figure 2).
At histology, the sizes of the carcinomas in all our
cases of PMiT ranged from 1 to 9 mm (median size of
3.16 mm). Seven patients (7/50 cases, 14%) showed
2 lesions with the appearance of PMiT. In such
cases, a diagnosis of multicentric PMiT was made.
Small papillary thyroid lesions ≤1cm
119 cases
PMiT
See Porto Proposal criteria
50/119 cases (42%)
“Incidental” PTMC
WHO 2004
Papillary carcinoma is found
incidentally and measures ≤1
cm diameter
59/119 cases (49.6%)
“Occult” PTMC
Despite their small size,
clinically present with
regional lymph nodes and
distant metastases
10/119 cases (8.4%)
Figure 1. Our experience (during the period from March
2003 to August 2007) on distribution of small (diameter ≤1 cm)
papillary thyroid lesions according to the 2004 WHO classifica-
tion and the Porto proposal criteria.
Furthermore, in 1 case, multicentric PMiTs were
localized in the right thyroid lobe (1 lesion) and in the
left thyroid lobe (1 lesion), whereas in 5 cases they
were in either of the thyroid lobes. PMiT was often
associated with chronic lymphatic thyroditis (10/50
cases, 20%), follicular adenoma (5/50 cases, 10%), and
both hyperplasic nodular and diffuse goiters (35/50
cases, 70%). Moreover, 2 patients with hyperplasic
nodular goiter also showed parathyroid adenoma (2/35
case, 5.7%), and 1 patient with diffuse goiter also pre-
sented a thymoma classified as B1 (according to the
2004 WHO classification; 1/35 case, 2.8%).
Patients with association of PMiT and chronic
lymphatic thyroditis were all females, with ages
ranging from 39 to 66 years (median age of 52 years)
at the time of presentation.
In our experience, ultrasound imaging was
unable to detect the area corresponding to the
PMiT, because the diameters of our PMiTs were too
small (3.16 mm median size).
All patients are alive and well after a median of
31.6 months of follow-up (range, 5-57 months).
Occult Papillary Thyroid
Microcarcinoma Cases
Despite their small size, 10 of the 119 cases of small
papillary thyroid lesions clinically presented with
regional lymph node metastases. The prevalence of
occult PTMC diagnosis was 0.7% (10/1407 cases) of
all the thyroid specimens analyzed at the
Department of Biomedical Sciences and Human
Oncology, University of Turin, during the period
from March 2003 to August 2007. At histology, the
majority of tumors (9/10, 90%) were located in the
subcapsular region and showed invasion of the thy-
roid capsule (5 cases had pT3N1a stage, and 4 cases
had pT3N1b stage). Six cases showed sclerosing
appearance, whereas 4 cases had classical and follic-
ular features. The sizes of occult PTMCs ranged
from 3 to 10 mm (median size of 7.9 mm). Two
patients (2/10 cases, 20%) showed multifocal
lesions. In such cases, a diagnosis of multicentric
occult PTMC was made. Occult PTMC was associ-
ated with both hyperplasic nodular and diffuse goi-
ter (8/10 cases, 80%) and with autoimmune thyroid
diseases (2/10 cases, 20%).
All patients are alive after a median of 23.5
months of follow-up (range, 12-54 months). In par-
ticular, 1 patient is alive with disease 15 months
after surgery and radioiodine treatment.
Incidental Papillary Thyroid
Microcarcinoma Cases
The WHO (2004 classification)1classified inciden-
tal PTCM as a papillary carcinoma that is found
incidentally and measures ≤1 cm in its major axis.
We diagnosed 59 cases of incidental PTCM, with
a prevalence of 4.2% (59/1407 cases) of all the
thyroid specimens analyzed at the Department of
Biomedical Sciences and Human Oncology,
University of Turin, during the period from March
2003 to August 2007. Those tumors had features
indicative of a potential for an aggressive behavior
(ie, invasion of the thyroid capsule, blood vessel
permeation, or tall cells features). At histology,
18/59 cases (30.5%) showed invasion of the thyroid
capsule; lymph node metastases were also observed
in 2 cases. Forty-one cases (69.5%) had pT1 stage
variously associated with multicentric lesions (≥1
cm when take together) in 21 cases, sclerosing or
tall cells features in 6 cases, areas of suspicious for
capsular or blood invasion in 13 cases, age ≤19 years
at presentation in 2 cases, and lymph nodes metas-
tases (pN1a) in 3 cases. Incidental PTMC was asso-
ciated with both hyperplasic nodular and diffuse
goiters (47/59 cases, 79.7%), to autoimmune thyroid
diseases (10/59 cases, 16.9%), and to parathyroid
adenoma (2/59 cases, 3.4%).
4International Journal of Surgical Pathology / Vol. XX, No. X, Month XXXX
0%
10%
20%
30%
40%
50%
60%
70%
80%
2003 2004 2005 2006 2007
Benign thyroid diseases
Malignant thyroid diseases
Papillary microtumors
Figure 2. The prevalence of PMiT at the Department of
Biomedical Sciences and Human Oncology, University of Turin,
during the period from March 2003 to August 2007.
Fifty-eight out of 59 patients (98.3%) are alive
after a median of 32.7 months of follow-up (range,
5-61 months). In particular, 1 patient was dead of
other causes soon after surgery, 1 patient is alive
with disease (bone metastases) 41 months after sur-
gery, and 1 patient showed local recurrence, surgically
removed, 12 and 24 months after thyroidectomy
(now the patient is alive and well 52 months after
the first surgery).
Discussion
The term microcarcinoma should be restricted to
papillary carcinomas that are found incidentally and
measure ≤1 cm in diameter.1These tumors have
been also referred to with various other terms,
including occult latent papillary carcinoma, nonen-
capsulated thyroid tumor, and occult sclerosing car-
cinoma, all of which should be avoided because they
are no longer applicable to describe a small lesion
(≤1 cm) found incidentally.
The incidence of thyroid cancer, particularly the
papillary forms, has been increasing sharply for
many years in Western countries. The reasons for
such an increase are not clear, but several authors
suggested that overdiagnosis might be involved.
Patients with PTMC represent up to 30% of all
differentiated thyroid carcinoma worldwide,
including in our series when PTMC and PMiT
were taken together. A subgroup of PTMC, desig-
nated as PMiT by Rosai et al,23 is likely to have a
benign biological behavior similar to that of clini-
cal benign thyroid diseases. The extent of diseases
and the variations in histological findings are criti-
cal factors that should dictate the therapeutic
strategy and follow up. The lack of long-term ran-
domized prospective studies makes it very difficult
to establish which therapeutic approach is better,
explaining the present uncertainty and controver-
sies on this subset of PTMC.
The crucial point is how to manage incidental
thyroid micronodules. Recently, at a European con-
sensus for the management of patients with differ-
entiated thyroid carcinoma, participants divided
patients into very low-risk group, low-risk group, and
high-risk group according to the postsurgical
radioiodine administration (following thyroid abla-
tion), with agreement reached on both the high-risk
group and the very-low-risk group. Indeed, in the
first group, postoperative 131I administration reduces
the recurrence and possibly prolongs survival,
whereas in the latter group, postoperative 131I
administration does not have indication and bene-
fits. Instead, for patients in the low-risk group, the
participants did not reach an agreement on thyroid
ablation after surgery.22 However, no definitive treat-
ment guideline was developed to indicate how best
to treat and manage these small tumors.
As a result, at present both surgeons and
patients become alarmed when pathologists report
the presence of carcinoma, which may lead to
reoperation (completion thyroidectomy after previ-
ous lobectomy, radioiodine treatment) or an
aggressive follow-up (substitutive therapy with
TSH suppression), all of which are deemed unnec-
essary. On the other end, the pathologist is bound
to define as a carcinoma a lesion with a most likely
benign clinical course. For these reasons, Rosai et
al23 proposed the term papillary microtumor of the
thyroid during the 12th Annual Cancer Meeting in
Porto and reported strict definition criteria for
such entities.
In our experience, based on 50 consecutive
cases, the PMiT terminology is well accepted by
both clinicians and patients.
This term, which aptly demarks a subset of tumors
roughly corresponding to half of the cases falling
under the definition of PTMC according to the WHO
classification,1decreases the danger of overtreatment,
minimizes the psychological anxiety engendered by a
diagnosis of carcinoma, and maintains unchanged the
patient’s eligibility for health insurance.
We would therefore advise the adoption of the
term PMiT. Our data are relevant inasmuch as it
clearly defines the boundaries and the merits of
the definition of PMiT on a homogeneous case
series.
We assume that our personal experience (in spite
of the few number of cases submitted to lobectomy
[3/50] and the short follow-up) would stimulate col-
lection of new cases with adequate follow-up, and we
favor a consensus of both pathologists and clinicians
on the definition of this subset of PTMC.
Acknowledgments
The authors thank Dr Marco Volante, Department
of Clinical and Biological Sciences, University of
Turin, and San Luigi Hospital, Orbassano, Torino,
Italy, for helping review this article.
PMiT (Papillary Microtumor): A Subset of PTMC / Asioli et al 5
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