The impact of rhabdoid differentiation on prognosis in patients with grade 4 renal cell carcinoma.

Abstract

494 Background: Renal cell carcinoma (RCC) with rhabdoid differentiation is thought to portend a poor prognosis, similar to RCC with sarcomatoid differentiation. Both rhabdoid and sarcomatoid differentiation are classified as grade 4 RCC based on the most recent International Society of Urological Pathology (ISUP) grading system. We sought to determine the prognostic value of rhabdoid differentiation in comparison to RCC with sarcomatoid differentiation, grade 4 RCC without rhabdoid or sarcomatoid differentiation, and grade 3 RCC. Methods: Using the Mayo Clinic Nephrectomy Registry, we identified 406 patients with ISUP grade 4 RCC and 1,758 patients with grade 3 RCC. A urologic pathologist reviewed all specimens to determine the presence of both rhabdoid and sarcomatoid differentiation. Associations of clinical and pathologic features with death from RCC were evaluated using Cox models. Results: Among the 406 grade 4 RCC tumors, 111 (27%) had rhabdoid differentiation and 189 (47%) had sarcomatoid differentiation, although only 28 (7%) demonstrated both rhabdoid and sarcomatoid differentiation. In multivariable analysis of grade 4 RCC tumors, the presence of rhabdoid differentiation was not associated with death from RCC (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 patients with grade 3 RCC (HR 2.45, p<0.001) and grade 3 RCC with necrosis (HR 1.62; p<0.001). Conclusions: This study confirms that RCC with rhabdoid differentiation is appropriately classified as grade 4. However, unlike sarcomatoid differentiation, the presence of rhabdoid differentiation in grade 4 RCC is not associated with an increased risk of death from RCC. Therefore, rhabdoid and sarcomatoid differentiation should not be grouped together when assessing risk in a patient with grade 4 RCC.