Clinical characteristics and survival outcomes of primary sarcoma of the kidney (PSK).

566 Background: Primary sarcoma of the kidney (PSK) is a rare malignancy. Clinical characteristics and survival outcomes of PSK have not been well studied. Methods: Patients with PSK were identified in the Surveillance, Epidemiology, End Results (SEER) database from year 2000 to 2020 by using the primary cancer site codes for kidney as well as histological codes (ICD-O-3) that matches the list of sarcoma histology found in the NCCN soft tissue sarcoma and bone cancer guidelines. Data for demographics, disease extent, median overall survival (OS), and treatment modality were obtained. Sarcomas mixed with non-sarcoma histology, such as carcinosarcoma and clear cell sarcoma, were included in the analysis. OS data of patients with renal cell carcinoma (RCC) were obtained for comparison. Results: A total of 260,569 patients with primary kidney neoplasms were identified in the SEER database; 864 (0.003%) had PSK and . The majority were Caucasian (62.1%) followed by Hispanics (19.6%) and African Americans (8.9%). The most common histology was leiomyosarcoma (23.1%), followed by clear cell sarcoma (15.1%), and liposarcoma (15%). Other histology types were synovial sarcoma (4.4%), Ewing sarcoma (4.2%), and carcinosarcoma (2.8%). Pure sarcomas (n=709, 82.1%) were more frequent than mixed sarcomas (n=155, 17.9%). Majority of patients with pure sarcoma (68.1%) were ≥ 50 years of age and the majority with mixed sarcoma (62.0%) were ≤ 10 years of age. Among the 823 patients with known extent of disease at diagnosis, 36.2%, 33.0%, and 30.8% had localized, locoregional, and distant metastatic disease, respectively. Lung (18.2%) was the most common site of metastasis followed by liver (10.4%) and bone (8.8%). OS of PSK was 42 months compared to 122 months seen with RCC (p< 0.001). OS for patients with localized, regional, and distant diseases were 145, 46, and 9 months, respectively (P<0.001 with all comparisons). Among the 855 patients with treatment data available, 65 (7.6%) received chemotherapy only, 436 (51.0%) received surgical resection only, 252 (29.5%) received both, and 102 (11.9%) received neither. Both chemotherapy and surgery were associated with longer OS. Those who received chemotherapy showed OS of 47 months compared to 42 months seen in the no chemotherapy group (P=0.003). As for surgical resection, OS of those who underwent surgery was 63 months compared to 6 months in those who did not (P<0.001). Conclusions: PSK is rare and associated with worse outcomes compared to RCC. While pure sarcomas of kidneys were more common in older populations, mixed sarcomas had a bimodal age distribution and the majority were young. Disease stages at the time of diagnosis were comparable among local, locoregional, and distant metastatic diseases, but patients with distant metastases had worse survival. Chemotherapy and surgical resection were associated with better survival.