Thyroid-like follicular carcinoma of the kidney: A report of two cases and literature review

There have only been a few reports of thyroid-like follicular carcinoma of the kidney (TLFCK) to date. In the present study, two patients with TLFCK are reported. Patient 1 was a 65-year-old male exhibiting repeated hematuria and right back pain. No tumors were located in the patient's thyroid or lungs. The physical examination revealed percussion tenderness over the right kidney region was noticed. Enhanced computed tomography (CT) indicated a right renal pelvic carcinoma, for which the patient underwent a radical right nephrectomy. Patient 2 was a 59-year-old male with a mass in the right kidney, located during a health examination and who exhibited no obvious clinical symptoms. The patient was clinically diagnosed with right renal carcinoma, confirmed by an enhanced CT. The patient underwent a radical right nephrectomy. The clinical features, imaging results, pathology, immune phenotypes, treatment and prognosis were analyzed. The associated literature was also reviewed. The cut surface of each tumor showed gray-white material with a central solid area, including scattered gray-brown necrotic and gray hemorrhagic areas and small cystic cavities. Microscopically, the arrangement of the tumor cells mimicked thyroid follicles with red-stained colloid-like material in the lumen. No renal hilar lymph node involvement was noted. The tumor tissue of patient 1 was immunohistochemically positive for vimentin, epithelial membrane antigen (EMA), cytokeratin (CK), CK7, and neuron specific enolase; and negative for CK34BE12, synapsin (Syn), CK20, cluster of differentiation 56 (CD56), CD10, Wilm's tumor-1 (WT-1), CD34, CD57, P53, CD99, thyroid transcription factor-1 (TTF-1), CD15 and thyroglobulin (TG); with a Ki-67 labeling index (LI) of 30%. The tumor tissue of patient 2 was immunohistochemically positive for vimentin, EMA, CK7 and CK20; and negative for CD56, CD10, WT-1, CD34, CD57, P53, CD117, TTF-1, CD15, CD99, TG, chromogranin A and Syn; with a Ki-67 LI of 20%. TLFCK is a rare renal tumor with low malignancy but medium invasiveness. It morphologically resembles thyroid follicular carcinoma but does not express TTF-1 or TG. Radical nephrectomy can achieve good patient outcomes.