Clear cell renal cell carcinoma with rhabdoid differentiation: report of 10 Chinese cases supporting a distinctive variant

This article describes 10 cases of adult clear cell renal cell carcinoma with rhabdoid differentiation (ccRCC-RD). The lesions all occurred in adult patients (age range 51-77 years, median 56 years), and a marked male predominance (7 males and 3 females) was noted. Six lesions were located in the right kidney, and 4 were located in the left. Histologically, the lesions consisted of rhabdoid areas and classical clear cell RCC areas. The rhabdoid areas occupied 5% to 80% of the kidney in each of the cases. The rhabdoid cells exhibited a round to polygonal shape with globular eosinophilic cytoplasmic inclusions, eccentric pleomorphic vesicular nuclei and prominent nucleoli, which were arranged in large sheets with solid and organoid patterns. One case also exhibited sarcomatoid differentiation. Tumor necrosis was observed in all cases. In all cases, clear cell areas were ISUP grade 3 or 4. The rhabdoid and clear cells exhibited similar immunohistochemical profiles, including CK8/18+, Vimentin+, epithelial membrane antigen (EMA)+, PAX8+, desmin-, and alpha-SMA-, which supports the notion that the rhabdoid and clear cells originate from the same clone and do not represent muscle metaplastic differentiation. The mean Ki-67 labeling index was increased in the rhabdoid areas (32%) compared with the clear cell areas (6%). Follow-up data were obtained from 9 cases. Three patients had lung and bone metastasis, 4 patients died from the tumors, and 1 patient had tumor recurrence. Our results indicate that ccRCC with rhabdoid differentiation exhibits aggressive biological behavior and support the notion that ccRCC-RD is a distinctive variant.