Chromophobe renal cell carcinoma-like thyroid carcinoma: possible misdiagnosis as metastatic renal cell carcinoma.

To date, multiple thyroid cancer variants have been reported. Herein, we report a rare case of chromophobe renal cell carcinoma-like thyroid carcinoma (CRETHCA) in a 60-year-old woman, for which the morphologic findings resembled those of chromophobe renal cell carcinoma (ChRCC). ChRCC of the kidney is characterized by large polygonal tumor cells with distinct cell borders, perinuclear clearing, multiple binucleate cells, and strongly positive immunostaining for paired box gene 8 (PAX8) and carbonic anhydrase IX (CA IX). In our case, the thyroid gland tumor was incidentally detected by routine medical screening without sufficient medical information; it showed similar histology and immunohistochemical features to ChRCC and was initially misdiagnosed as metastatic ChRCC. Additional tests, including kidney computed tomography and positron emission tomography, revealed no abnormalities in the patient's kidney; therefore, we diagnosed the tumor as CRETHCA. Focal weak staining for thyroid transcription factor 1 (TTF-1) was the only supporting evidence that it was a primary thyroid neoplasm. To the best of our knowledge, this is the second report of CRETHCA in literature. This novel variant is very difficult to distinguish from metastatic ChRCC and can be a diagnostic challenge for pathologists. Further studies of similar cases should be done to define this new entity.