# Solid Subtype of Papillary Thyroid Carcinoma: A Case Series Highlighting Aggressive Features

## TL;DR

This case series shows that the solid subtype of papillary thyroid cancer can behave aggressively, especially in young patients, and may require more careful diagnosis and treatment.

## Contribution

The study presents three cases showing that solid subtype papillary thyroid carcinoma may be more aggressive than currently classified.

## Key findings

- Two patients had aggressive clinical courses with lymphatic metastases and possible distant spread.
- Immunohistochemistry showed consistent positivity for cytokeratin 7, thyroglobulin, TTF-1, and PAX8.
- The study suggests that current WHO classification may underestimate the aggressiveness of this subtype.

## Abstract

Papillary thyroid carcinoma (PTC) is the most common malignant thyroid neoplasm. Its solid/trabecular subtype (STPTC) is rare, and its aggressiveness remains controversial. We describe the clinical, histopathological, and immunohistochemical characteristics of three STPTC cases, highlighting their biological behavior and impact on current classification. Two patients exhibited aggressive clinical courses with extensive lymphatic metastases and possible distant spread, while the third case showed a more indolent progression. Immunohistochemistry revealed positivity for cytokeratin 7, cytokeratin 19, thyroglobulin, TTF‐1, and PAX8, with negativity for CD56, synaptophysin, and p63, among others. Although the 2022 WHO classification does not consider STPTC an aggressive subtype, the literature and our findings suggest reconsideration. Immunohistochemistry and the Ki‐67 proliferation index may be key tools for differential diagnosis and prognosis. STPTC can exhibit aggressive behavior, particularly in young patients. Early diagnosis and individualized therapeutic approaches are essential to improve clinical outcomes.

The solid subtype of papillary thyroid carcinoma may exhibit aggressive clinical behavior, particularly in young patients, with extensive lymph nodes and distant metastases. Recognizing this pattern is essential for accurate diagnosis and for guiding personalized treatment and follow‐up, despite its current non‐aggressive classification in the WHO guidelines.

Hematoxylin and eosin (H&E) stained section, 40×. Tumor cells with “Orphan Annie eye” nuclei arranged in solid nests.