Thyroid gland
Papillary thyroid carcinoma
Main variants
Microcarcinoma


Topic Completed: 4 August 2020

Minor changes: 22 September 2020

Copyright: 2003-2020, PathologyOutlines.com, Inc.

PubMed search: papillary thyroid carcinoma [title] microcarcinoma variant

Nadine Demko, M.D.C.M., M.Sc.
Marc Pusztaszeri, M.D.
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Cite this page: Demko N, Florianova L, Pusztaszeri M. Microcarcinoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/thyroidmicrocarcinomavariant.html. Accessed September 30th, 2020.
Definition / general
  • Papillary thyroid carcinoma (PTC) of ≤ 1 cm
  • 2017 World Health Organization definition based only on tumor size (irrespective of it being incidental or not)
Essential features
  • The most common variant of papillary thyroid carcinoma in the United States
  • The majority are indolent but some can exhibit malignant behavior
  • No definite biological or clinical parameters currently exist to distinguish indolent from potentially aggressive papillary thyroid microcarcinoma
  • Active surveillance may be considered as an alternative to surgery for a select group of patients with low risk tumors
Terminology
  • Synonym: papillary microtumor
  • Formerly called occult sclerosing carcinoma, occult papillary carcinoma and nonencapsulated sclerosing tumor
ICD coding
  • ICD-10: C73 - malignant neoplasm of thyroid gland
  • ICD-O: 8341/3 - papillary microcarcinoma
Epidemiology
Sites
  • Thyroid
  • Exceedingly rare at other sites (see Case reports below)
Pathophysiology
Etiology
Diagrams / tables

Images hosted on other servers:

Incidence and prognosis

Clinical features
Diagnosis
  • Histopathologic evaluation of thyroid resection specimens
  • Fine needle aspiration cytology (FNAC)
Laboratory
  • Recurrent disease (especially after total thyroidectomy) may be monitored by recombinant human TSH (rhTSH) stimulated serum thyroglobulin measurement, with or without neck ultrasound (J Clin Endocrinol Metab 2003;88:3668)
Radiology description
  • On ultrasonography: irregular nodule shape, aspect ratio (anteroposterior to transverse diameter of the nodule) of ≥ 1, unclear nodule boundary, blurred margins, internal heterogeneous hypoechogenicity, microcalcifications (Oncol Lett 2016;12:2451)
Radiology images

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Ultrasound

Prognostic factors
  • Excellent prognosis overall
  • Most represent a nonprogressive, clinically innocuous disease (self limiting cancer)
  • Small proportion have an aggressive clinical behavior; these represent early stages of papillary thyroid carcinoma that would eventually present as larger tumors
  • Meta analysis of 11 studies showed means of 7.2% for microscopic extrathyroidal extension, 28% for lymph node metastases, 0.7% for distant metastases, 5% for tumor recurrence and 0.3% for tumor related death (Endocr Pract 2007;13:498)
  • No definite biological or clinical parameters currently exist to distinguish low risk indolent from potentially aggressive tumors
  • Meta analysis of 17 studies revealed that recurrence was associated with younger age (< 45 years), tumor multifocality and lymph node metastasis at presentation, whereas no association with gender, tumor size and extrathyroidal extension was found (Eur J Endocrinol 2008;159:659)
  • BRAF V600E mutation may be associated with aggressive disease but, as an isolated element, cannot identify cases that will spread locoregionally or to distant sites (Ann Surg Oncol 2009;16:240, Eur J Cancer 2020;124:161)
  • Coexistence of BRAF with other oncogenic mutations (PIK3CA, AKT1, TERT promoter or TP53) mutations may indicate a less favorable outcome (Thyroid 2016;26:1)
Case reports
Treatment
  • No consensus on treatment but generally similar to thyroid carcinomas > 1 cm, depending on the lymph node status and other clinical factors
  • Thyroid lobectomy alone is sufficient treatment for small, unifocal, intrathyroidal carcinomas in the absence of prior head and neck radiation, familial thyroid carcinoma or clinically detectable cervical nodal or distant metastases (Thyroid 2016;26:1)
  • Active surveillance may be considered as an alternative to surgery in selected patients with low risk tumors without clinically evident lymph nodes metastases or local invasion (Eur J Surg Oncol 2018;44:307, Cancer 2017;123:372, Thyroid 2016;26:1)
  • Diagnosis of incidental papillary thyroid microcarcinoma in thyroid resection specimens is not, by itself, an indication for additional treatment (i.e. surgery, radioactive iodine)
Gross description
  • White-gray fibrotic nodule with irregular contours or an ill defined light brown nodule, measuring ≤ 1 cm
  • Multifocality in 20 - 46% (World J Clin Cases 2020;8:1350, Adv Anat Pathol 2006;13:69)
  • Due to their small size, these lesions can be easily missed on gross examination and are often identified only microscopically
Gross images

AFIP images

Well circumscribed tumor of < 2 mm

Small irregular fibrotic tumor

Frozen section description
  • Frozen section is usually not indicated
Microscopic (histologic) description
  • Defined solely by the ≤ 1 cm size criterion; does not have a unique morphology
  • Overall varied architectural patterns with characteristic nuclear features of papillary thyroid carcinoma
  • Typically shows an irregular stellate or scar-like configuration
  • May be nonencapsulated or encapsulated, with or without a sclerotic rim
  • Composed of papillary or follicular structures or a mixture of both
  • Follicular pattern more common than a pure papillary (classical) pattern (Adv Anat Pathol 2006;13:69)
  • Characteristic nuclear attributes are present at high power: nuclear enlargement and overlapping, chromatin clearing, irregular nuclear contour, nuclear grooves and nuclear pseudoinclusions
  • May show cytologic or architectural features of several variants, including follicular or tall cell
Microscopic (histologic) images

Contributed by Nadine Demko, M.D.C.M., M.Sc., Livia Florianova, M.D., M.Sc. and Marc Pusztaszeri, M.D.

Follicular architecture

Nuclear features

Irregular contour with dystrophic calcification

Nuclear features

Infiltrative pattern

Tall cell features


Chronic thyroiditis background

Follicular architecture

Nuclear features

Tall cell features

Minimal extrathyroidal extension


Infiltrative pattern

Nuclear features

BRAF V600E



Contributed by Andrey Bychkov, M.D., Ph.D.

CK19, galectin3 and HBME1

Incidental finding in multinodular goiter

Encapsulated papillary microcarcinoma

Virtual slides

Images hosted on other servers:

Tall cell features

Cytology description
  • Usually incidental and is not sampled by fine needle aspiration cytology
  • However, some of these lesions undergo fine needle aspiration cytology because of suspicious radiology findings (multifocality, calcification, etc.) or in patients with a history of radiation to the head and neck region to establish the diagnosis and to determine the most appropriate management
  • May be accidentally sampled during the aspiration of other clinically significant thyroid nodules (Acta Cytol 2001;45:341)
  • Cytologic features are essentially the same as for papillary thyroid carcinoma (Int J Surg Pathol 2002;10:133, Acta Cytol 2001;45:341)
Cytology images

Contributed by Nadine Demko, M.D.C.M., M.Sc., Livia Florianova, M.D., M.Sc. and Marc Pusztaszeri, M.D.

Cytological features



Contributed by Grace C.H. Yang, M.D.

Pap stained slides

Positive stains
Negative stains
Molecular / cytogenetics description
  • Similar mutations as papillary thyroid carcinoma > 1 cm
  • BRAF V600E mutation in 30 - 67% (Thyroid 2016;26:1)
Videos

Active surveillance

Sample pathology report
  • Thyroid, right lobe, right hemithyroidectomy:
    • Incidental papillary thyroid microcarcinoma, 3 mm, negative for lymphatic invasion and extrathyroidal extension; resection margin negative
  • Thyroid, total thyroidectomy:
    • Papillary thyroid microcarcinomas, x 5, bilateral, measuring up to 8 mm, negative for lymphatic invasion and extrathyroidal extension; resection margin negative
Differential diagnosis
Board review style question #1

Which of the following statements about papillary thyroid microcarcinoma (shown in the image) is correct?

  1. Can always be diagnosed on cytology alone
  2. Can contain tall cell features
  3. More likely to show a pure papillary rather than follicular architecture
  4. Must be incidental and measure ≤ 1 cm
  5. Requires a total thyroidectomy
Board review answer #1
B. Can contain tall cell features. Papillary thyroid microcarcinoma may show features of other variants including tall cell. Tall cell features should be recognized and reported since they are associated with more aggressive behavior. The other answer choices are incorrect because the 2017 World Health Organization definition is based only on tumor size (irrespective of it being incidental or not), the final size is most often determined on a surgical resection specimen (though it may also be estimated by ultrasound), follicular architectural pattern is more common than pure papillary (classical) pattern and may be managed by a lobectomy or active surveillance.

Comment Here

Reference: Papillary thyroid microcarcinoma (PTMC)
Board review style question #2
Which of the following immunostains is usually not expressed in papillary thyroid microcarcinoma?

  1. BRAF V600E
  2. CK19
  3. Galectin3
  4. HBME
  5. p63
Board review answer #2
E. p63. Papillary thyroid microcarcinoma is usually negative for p63, in contrast to the mimicker solid cell nests which are usually positive for p63. HBME, galectin3 and CK19 are expressed in most and can be used to support the diagnosis. BRAF V600E immunostain is often expressed and can be used as a reliable surrogate marker for the corresponding BRAF V600E gene mutation, present in 30 - 67%.

Comment Here

Reference: Papillary thyroid microcarcinoma (PTMC)
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