Thyroid & parathyroid

• Borderline follicular cell derived tumor that does not fulfill all criteria for malignancy, classified under thyroid tumors with uncertain malignant potential (UMP) as a new tumor entity in the 4th and 5th editions of the WHO classification of thyroid tumors (Pathol Int 2018;68:641)
• Encapsulated, follicular patterned thyroid tumor with questionable capsular or vascular invasion and absence of papillary thyroid carcinoma (PTC) type nuclear features

• Should be diagnosed only by histopathological evaluation, after complete examination for capsular and vascular invasion
• Nonspecific fine needle aspiration (FNA) cytology or imaging findings, often showing indeterminate cytology (Bethesda III / IV) or sonography features such as a well circumscribed iso / hypoechoic solid nodule with peripheral vascularity

Images hosted on other servers:

• Simple thyroid lobectomy with long term postsurgery active surveillance (Gland Surg 2018;7:S8)
• No radioactive iodine is required (Endocr J 2022;69:757)

Images hosted on other servers:

Contributed by Mohammad Tavangar, M.D.

Images hosted on other servers:

• TTF1
• PAX8
• Thyroglobulin
• Low molecular weight keratins
• EMA
• Low proliferative index (Ki67 < 5%)
• Very heterogeneous immunohistochemical profile for HBME1, cytokeratin 19, galectin3 and CD56, which is not helpful in differentiation from follicular carcinoma based on limited available studies but may be used to distinguish follicular neoplasm from follicular variant papillary carcinomas (and noninvasive follicular thyroid neoplasm with papillary-like nuclear features [NIFTP]) (Mod Pathol 2005;18:541, Pathol Res Pract 2015;211:320)

• Thyroid gland, right lobectomy:
  • Encapsulated follicular patterned thyroid nodule, in favor of follicular tumor of uncertain malignant potential (FT-UMP) (see comment)
  • Tumor site: right lobe
  • Tumor size: 15 mm in greatest dimension
  • Comment: Sections show an encapsulated thyroid nodule composed of follicular cells mostly arranged in microfollicles. The cells have hyperchromatic small nuclei with scant clear to eosinophilic cytoplasm. Rare mitotic figures are seen. A focus suspicious for capsular invasion with irregular infiltration of the capsule by tumor cells (but without full thickness interruption of the capsule) is identified.

• Follicular carcinoma:
  • Definite or true vascular or capsular invasion
  • Extrathyroid extension
  • Similar IHC and molecular features
  • Ki67 may be helpful (> 10%) (Endocr J 2015;62:1)
• Follicular adenoma:
  • No capsular or vascular invasion
  • Similar IHC and molecular features
• Thyroid well differentiated tumor of uncertain malignant potential (WDT-UMP):
  • Follicular patterned encapsulated thyroid nodule
  • Questionable or equivocal nuclear changes of papillary thyroid carcinoma (incomplete nuclear changes that fall short of a diagnosis of papillary carcinoma)
• Follicular variant of papillary thyroid carcinoma:
  • Obvious nuclear changes of papillary thyroid carcinoma (nuclear grooves, intranuclear pseudoinclusions and nuclear clearing)
  • IHC for HBME1, cytokeratin 19, galectin3 and CD56 may be used to distinguish follicular neoplasm from follicular variant papillary carcinomas (Mod Pathol 2005;18:541, Pathol Res Pract 2015;211:320)
• Thyroid follicular nodular disease (nodular goiter) with dominant nodule:
  • Not encapsulated or incomplete capsule
  • Cytoarchitectural pattern similar to surrounding thyroid tissue
  • May be multiple
  • Lack of compression signs in adjacent thyroid gland
• Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP):
  • Follicular patterned encapsulated thyroid nodule
  • Nuclear alterations of papillary thyroid carcinoma with a nuclear score of 2 or 3 (JAMA Oncol 2016;2:1023)

Microscopic examination of a 20 mm well defined encapsulated thyroid nodule shows dominant microfollicular structures composed of follicular cells with small round nuclei, heterogenous chromatin pattern and clear to eosinophilic cytoplasm. No mitosis is seen. Few capsular large vessels with floating clusters of tumor cells within the lumen without thrombus formation are also noted. No evidence of capsular invasion is identified. What is the most likely diagnosis?

1. Follicular adenoma
2. Follicular carcinoma
3. Follicular tumor of uncertain malignant potential (FT-UMP)
4. Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)
5. Well differentiated tumor of uncertain malignant potential (WDT-UMP)

C. Follicular tumor of uncertain malignant potential (FT-UMP) is a follicular patterned thyroid tumor with questionable (not definite) vascular invasion. Answer B is incorrect because follicular carcinoma requires definite capsular or vascular invasion, which is absent in this case. Answer E is incorrect because well differentiated tumor of uncertain malignant potential (WDT-UMP) is associated with suspicious papillary carcinoma-like nuclear changes, which are not seen here. Answer A is incorrect because follicular adenoma does not show any vascular or capsular invasion, even equivocal. Answer D is incorrect because noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) demonstrates nuclear features of papillary thyroid carcinoma, which are not present in this case.

Comment Here

Reference: FT-UMP

Which of the following is true for thyroid follicular tumors of uncertain malignant potential (FT-UMP)?

1. Equivocal nuclear features of papillary thyroid carcinoma
2. Follicular patterned thyroid tumor with atypical follicular cells and increased mitosis
3. Follicular patterned thyroid tumor with questionable vascular or capsular invasion
4. Follicular thyroid tumor with definite capsular invasion
5. Follicular thyroid tumor with extrathyroid extension

C. Follicular patterned thyroid tumor with questionable vascular or capsular invasion. Thyroid follicular tumor of uncertain malignant potential is characterized by follicular cells having bland looking nuclei without nuclear features of papillary thyroid carcinoma, arranged in follicular structures and equivocal capsular or vascular invasion. Answer A is incorrect because FT-UMP lacks nuclear features of papillary thyroid carcinoma. Answer E is incorrect because FT-UMP does not exhibit extrathyroid extension, a feature of follicular carcinoma. Answer D is incorrect because FT-UMP only shows questionable, not definite, capsular invasion. Answer B is incorrect because FT-UMP generally lacks significant nuclear atypia and increased mitosis.

Comment Here

Reference: FT-UMP