Changes in treatment (Rx) patterns and attrition rates in patients (pts) with metastatic clear cell renal cell carcinoma (mccRCC).

4527 Background: Rx landscape of mccRCC has evolved rapidly with the approval of antibodies directed against programmed cell death protein-1 (PD-1) in combination with cytotoxic T-lymphocyte-associated protein 4 (CTLA4) or vascular endothelial growth factor receptor tyrosine kinase (TKI) inhibitors. However, real-world data on Rx trends and attrition before and after PD-1 inhibitor approval are lacking. Herein, we analyze them in a large real-world cohort in the United States. Methods: This IRB-approved retrospective study used the nationwide Flatiron Health electronic health record (EHR)-derived de-identified database. Inclusion: Metastatic RCC with clear cell histology diagnosed between 1/1/2011 to 1/31/2022 receiving Rx with opportunity of at least 1 year follow up. Exclusion: Pts needing Rx for ≥2 malignancies. Based on the approval date of PD-1+CTLA4 of 4/16/18, pts were separated into 2 groups: b2018 (1L Rx before 4/16/2018) and a2018 (1L Rx after 4/16/18). Landmark analysis was performed at 1 year after Rx discontinuation to identify pts who died, were alive but did not need Rx, or starting next-line Rx. All analysis was done using R version 4.2.3. Results: Of 12707 pts, 7923 met the eligibility criteria (b2018: 4561 pts and a2018: 3362 pts). Rx trends are summarized in the table. 1L Rx for the majority of pts changed from TKI monotherapy (mono; 79%) b2018 to PD-1 combination therapies a2018 (58%). TKI mono remained the most common Rx in both groups after 1L (Table). In the b2018 cohort, 58% of patients received 2L Rx, and 32% received 3L. In the a2018 cohort, 42% and 16% received 2L and 3L, respectively. At 1-year landmark analysis after 1L discontinuation: in the b2018 group, 58% pts received next Rx, 30% died without further Rx, and 12% were alive without Rx while in the a2018 group, 42% pts received next Rx, 26% died without further Rx and 32% were alive without Rx. Conclusions: Despite the increase in the utilization of PD-1+CTLA-4 and PD-1+TKI regimens since 2018, a significant number of patients still did not receive novel combination regimens in the 1L mccRCC setting in this real-world population in the United States. Furthermore, with the uptake of PD-1 based combinations in 1L, a higher proportion of pts experience treatment free interval or were alive without further therapy at 1 year landmark analysis after 1L Rx discontinuation. These findings need validation in other datasets and can help patient counseling in clinics.[Table: see text]