Thyroid follicular carcinoma-like tumor of kidney: a case report with morphologic, immunohistochemical, and genetic analysis.

We present an unusual renal tumor, which has not been classified under a known subtype of renal cell carcinoma (RCC) and characteristically shows similar histology to thyroid follicular carcinoma. The patient was a 32-year-old asymptomatic woman who was found to have a kidney mass during her annual physical examination. She had no lesions in the thyroid during physical and ultrasound examinations, and there was no abnormal thyroid function test. Neither mediastinal nor ovarian abnormalities were observed. The resected kidney showed a well-defined nodular tumor measuring 11.8x8.0x8.0 cm. The mass was protruding into the pelvic cavity with areas of yellowish geographic necrosis. Histologically, the tumor showed follicular architectures with inspissated colloid-like material in their lumina. No conventional (clear cell) RCC or any other known subtypes of RCC component was observed. Immunohistochemically, the tumor cells showed intensive staining for cytokeratin (CK) cocktail AE1/AE3 and CD10 and were not reactive to thyroid transcription factor-1 and thyroglobulin. The staining of CK35betaH11 and vimentin revealed focal cytoplasmic reaction. The tumor cells were completely negative for CK7, CK19, CK20, CK34betaE12, carcinoembryonic antigen, epithelial membrane antigen, and CD15. Chromosomal gains of 7q36, 8q24, 12, 16, 17p11-q11, 17q24, 19q, 20q13, 21q22.3, and Xp and losses of 1p36, 3, and 9q21-33 were detected by comparative genomic hybridization. These findings are dissimilar to previously classified renal neoplasm. Only a report that included three cases of primary thyroid-like renal tumor has been described in the abstract form. However, there is no fully documented case on this unusual form of RCC, which morphologically resembles that of thyroid follicular carcinoma. Herein, we present a new case of thyroid follicular carcinoma-like tumor of the kidney with a chromosomal study and review of the literature.