Encapsulated malignant follicular cell-derived thyroid tumors.

Area of Science:

• Endocrinology
• Oncology
• Pathology

Background:

• Encapsulated malignant follicular cell-derived thyroid tumors, including encapsulated follicular variant of papillary thyroid carcinoma (FVPTC) and encapsulated follicular carcinoma (EFC), present diagnostic challenges.
• FVPTC can be encapsulated or infiltrative, with encapsulated forms rarely metastasizing to lymph nodes, unlike infiltrative tumors.
• EFC outcomes are generally good, but angioinvasion can lead to recurrence and metastasis.

Purpose of the Study:

• To clarify the distinct clinical behavior and molecular profiles of encapsulated FVPTC and EFC.
• To differentiate between indolent and potentially aggressive encapsulated thyroid tumors.
• To guide appropriate treatment strategies for these controversial tumor types.

Main Methods:

• Comparative analysis of clinical presentation, histopathological features, and molecular profiles (RAS and BRAF mutations) of FVPTC and EFC.
• Review of treatment outcomes, including recurrence and metastasis rates.
• Evaluation of the impact of angioinvasion on EFC prognosis.

Main Results:

• Encapsulated FVPTC shares molecular similarities with follicular adenomas/carcinomas (high RAS, absent BRAF) and exhibits indolent behavior, especially when noninvasive.
• Infiltrative FVPTC shows a molecular profile closer to classical papillary thyroid carcinoma (BRAF > RAS mutations) and frequently metastasizes to lymph nodes.
• EFC with extensive angioinvasion demonstrates a significant rate of distant recurrence, challenging its classification as minimally invasive.

Conclusions:

• Noninvasive encapsulated FVPTC warrants conservative management due to its indolent nature.
• EFC with extensive angioinvasion should not be termed minimally invasive to ensure adequate patient treatment and prevent undertreatment.
• Accurate histopathological classification and molecular profiling are crucial for distinguishing between indolent and aggressive encapsulated thyroid tumors.