Effect of immunotherapy (IO) on primary renal tumor in metastatic renal cell cancer (mRCC).

649Background: Recent data showed that cytoreductive nephrectomy (CN) should not be performed prior to systemic therapy in intermediate and poor risk groups. Immune checkpoint inhibitors (ICI) are now approved in first and second line in mRCC, but ICI effect on the primary tumor is unknown. Methods: All patients (pts) treated with ICI for mRCC without prior CN were retrospectively collected and sequential computed tomography (CT) scan evaluated for response. Primary objective was Objective Response Rate (ORR) in the primary renal tumor in the primary RECIST 1.1. Secondary objective included systemic ORR and nephrometry score changes. Results: A total of 20 pts were treated with ICI with primary tumor in situ between 12/2012 and 10/2018. Among these, CT scans were available for evaluation of response for 19 primary tumors in 18 pts. Median age was 59.5 years. Pathology was 16 clear cell RCC, 2 translocation RCC, 1 Collecting duct carcinoma. Baseline median primary renal tumor size was 7.3 cm. ICI was used ...