Histologic Heterogeneity of Metastases in Clear Cell Renal Cell Carcinoma with Sarcomatoid Differentiation

Background/Objectives: Sarcomatoid or rhabdoid renal cell carcinoma (sRCC) represents an aggressive dedifferentiated phenotype of RCC associated with high metastatic potential. The histologic composition of metastatic lesions arising from clear cell RCC with sarcomatoid/rhabdoid differentiation (ccRCC/sRCC) and its relationship to the primary tumor remain incompletely characterized. Methods: We retrospectively reviewed patients undergoing nephrectomy for ccRCC/sRCC who had at least one resected metastatic lesion between 2013 and 2025 at a single institution. Primary and metastatic lesions were characterized by the percentage of clear cell versus sarcomatoid/rhabdoid histology. Associations between sarcomatoid/rhabdoid percentage in the primary tumor, metastatic histology, metastatic location, and overall survival were examined. Results: Twenty-six patients with 63 metastases were included. Metastatic histology demonstrated substantial heterogeneity, with 27 lesions (43%) showing pure clear cell histology, 21 (33%) mixed, and 15 (24%) pure sarcomatoid/rhabdoid. Some patients had multiple metastases with differing histology. Increasing sarcomatoid/rhabdoid percentage in the primary was associated with a higher likelihood of sarcomatoid/rhabdoid in metastases (p < 0.001). ROC analysis demonstrated primary tumor sarcomatoid/rhabdoid percentage predicted sarcomatoid/rhabdoid differentiation in metastases (AUC 0.84, 95% CI 0.73–0.95). An optimal cutoff of 10% sarcomatoid/rhabdoid differentiation predicted sarcomatoid/rhabdoid features in metastases. Metastatic histology varied by site, with lymph node metastases more frequently demonstrating clear cell morphology and visceral metastases more commonly exhibiting sarcomatoid/rhabdoid features. Conclusions: Metastases arising from ccRCC with sarcomatoid/rhabdoid differentiation exhibit marked histologic heterogeneity. These findings highlight the complex biology of ccRCC/sRCC metastasis and underscore the need for studies examining molecular drivers of metastatic heterogeneity, as well as the relationship between metastatic histology and therapeutic response.