Impact of Rhabdoid Differentiation on Prognosis for Patients with Grade 4 Renal Cell Carcinoma

Renal cell carcinoma (RCC) with rhabdoid differentiation is thought to portend a poor prognosis, similar to RCC with sarcomatoid differentiation. Both features are currently classified as grade 4 RCC based on the most recent International Society of Urological Pathology (ISUP) grading system. We reviewed a large series of patients with grade 4 RCC to determine the differential effects of rhabdoid and sarcomatoid differentiation on patient outcome. We identified 406 patients with ISUP grade 4 RCC including 111 (27%) with rhabdoid differentiation. In multivariable analysis of grade 4 RCC tumors, the presence of rhabdoid differentiation was not associated with death from RCC (hazard ratio [HR]: 0.95; p = 0.75); in contrast, sarcomatoid differentiation was significantly associated with death from RCC (HR: 1.63; p < 0.001). Patients with RCC with rhabdoid differentiation were significantly more likely to die of RCC than a comparison cohort of 1758 patients with grade 3 RCC (HR: 2.45; p < 0.001). The novel findings of our study suggest that rhabdoid and sarcomatoid differentiation should not be grouped together when assessing risk in a patient with grade 4 RCC but support the notion that rhabdoid differentiation is appropriately placed in the ISUP grade 4 category.