642
Background: Across a variety of malignancies, sites of metastatic involvement are known to be associated with differences in survival. We sought to characterize the frequency and survival of patients with different sites of metastases in mRCC. Methods: Patients with mRCC starting treatment between 2002-2019 were identified and sites of metastatic involvement at time of systemic therapy initiation were documented. The primary outcomes of interest were prevalence of metastatic site involvement and overall survival (OS). Multivariable Cox regression models were performed to adjust for imbalances in IMDC risk factors. Results: A total of 10,320 patients were included. Median age at diagnosis was 60, 73% were male, 87% had clear-cell histology and 80% underwent nephrectomy. The most common sites of metastases were: lung (71%), lymph nodes (49%), bone (36%), liver (21%), adrenal (9%), brain (9%), pancreas (5%), pleura (4%) and thyroid (0.6%). Survival by metastatic site and adjusted hazard ratios are presented in Table. Conclusions: Metastases to endocrine organs (pancreas, thyroid, adrenal) are infrequent but are associated with the longest median OS, whereas bone, liver, pleura and brain metastases are associated with median OS < 18 months. These benchmark values are useful for patient counseling and study design. Sites of metastatic involvement may reflect differences in underlying disease biology, and further work to investigate differences in immune, molecular and genetic profiles between metastatic sites is encouraged.[Table: see text]