Thyroid-like Follicular Carcinoma of the Kidney and Papillary Renal Cell Carcinoma with Thyroid-like Feature: Comparison of Two Cases and Literature Review.

Thyroid-like follicular carcinoma of the kidney (TLFCK) is a provisional new entity of renal cell carcinoma (RCC). We herein reported and compared one TLFCK case and one PRCC case with thyroid-like feature. The former entirely consisted of thyroid-like follicular architecture and the tumor cells were diffusely positive for PAX-8, but negative for CK7, AMACR, and CD10. By contrast, both papillary architecture (~60%) and thyroid-like follicular architecture (~40%) were identified in the latter. Tumor cells in both histological components exhibited diffusely positive staining for PAX-8, CK7, AMACR, but negative for CD10. FISH analysis showed no aberration in TLFCK case but trisomy of chromosome 17 in PRCC case. Along with a brief literature review, we presented that recognition of TLFCK is important to distinguish it from other conditions that show thyroid-like features. Additionally, a diagnosis of TLFCK should be cautiously made when papillary component is present in the tumor.