Abstract:

Thyroid-like follicular carcinoma of the kidney (TLFCK) is an extremely rare subtype of renal cell carcinoma (RCC) that histologically mimics primary follicular carcinoma of the thyroid gland. This new entity has not yet been integrated into the current WHO classification of renal tumors due to the limited data available. We report a further case of this rare histological entity, discuss the clinical, histological and immunohistochemical findings and provide an update on the review of the literature. A 73-year-old woman was found to have a left renal mass during her annual medical checkup. Her past medical history included high blood pressure and renal failure at hemodialysis stage. The patient underwent a nephrectomy with simple postoperative course. The tumor was described as being round, well circumscribed and dark brown in color. Histologically, the tumor showed follicular architecture with macro and micro follicles containing eosinophilic secretions or colloid-like material. Immunohistochemical studies demonstrated that the tumor cells exhibited no immunoreactivity for thyroid transcription factor-1 and thyroglobulin. The tumor cells showed intensive staining for cytokeratin 7 (CK7). The tumor cells were completely negative for CK20, WT1 and PAX8. Molecular biology was not carried out for lack of means. These findings are dissimilar to previously classified renal neoplasm. Thyroid-like follicular renal cell carcinoma represents a unique histologic subtype of renal cell carcinoma of low malignant potential and its primary importance is to distinguish it from metastatic carcinoma from the thyroid. A correct histopathologic diagnosis has important clinical and therapeutic implications. The current consensus from ISUP is not to recommend TLFCK as a new WHO histologic classification due to the small number of cases therefore, documentation of all cases available seems to be important to gain additional knowledge.

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