Unravelling the Aggressive Nature of Renal Cell Carcinoma Subtype with Rhabdoid Differentiation: A Series of Six Cases

Rhabdoid differentiation has been described in various carcinomas involving different organs and is recognised as a marker of aggressive tumour behaviour. In Renal Cell Carcinoma (RCC), the current grading system of the International Society of Urologic Pathology (ISUP) has given the highest grade IV to renal cell carcinoma with rhabdoid differentiation, signifying the worst prognosis. This article delineates 6 cases of clear cell RCC with rhabdoid differentiation over four years. All patients were male with a median age of 57.5 years. Microscopically, the tumour showed clear cell areas with rhabdoid differentiation occupying 10 to 45% of tumour volume. One of the six cases showed metastasis to the small bowel at the time of presentation, highlighting the aggressive clinical course. Immunohistochemical evaluation of Ki67 labelling index ranging from 25 to 50%. Our study highlights the significance of rhabdoid differentiation in clear cell renal carcinoma, which is seen rarely but indicates aggressive behaviour.