Evaluation of body weight and race on pembrolizumab response in patients with endometrial cancer: A case control study.

e17579 Background: Recent studies demonstrate improvement in PFS when pembrolizumab, a humanized monoclonal antibody (mAB) that inhibits the PD-1 receptor, is used with platinum-based regimens for advanced or recurrent endometrial cancer (EC). ASCO recommends studies evaluate the effect of weight on efficacy of anticancer agents to guide dosing. In addition, most studies evaluating the pharmacokinetic effects of mABs typically include only white patients. Pembrolizumab is administered at a flat dose and there are currently no adjustments for weight or race. Therefore, this study was performed to evaluate the impact of weight and race on outcomes in patients with EC treated with pembrolizumab. Methods: This retrospective IRB-approved case-control study included EC patients from 04/2014-12/2022 treated with pembrolizumab. Any patient >18 years with EC who received pembrolizumab was included; carcinosarcoma excluded. Chart review was performed. Response was recorded using RECIST criteria and based on imaging and/or primary oncologist’s determination. Associated toxicities were graded by CTCAE. Statistical testing performed as appropriate. Results: Fifty patients met inclusion criteria, with a mean age of 66.0 years. The majority presented with advanced EC (Stage III or greater) at diagnosis (n=33, 66%). Twenty-eight (56%) had endometroid histology, and 42% (n=21) were MMRd. Most patients received single-agent pembrolizumab (n=26; 52%) or pembrolizumab with lenvatinib (42%), with an average of 8.44 cycles (either 200 mg every 3 weeks or 400 mg every 6 weeks). The table details the objective response rate (ORR) and PFS for patients by race and weight. There was no significant difference in PFS between non-obese (normal weight + overweight) and obese (obese + severely obese) overall. Conclusions: No difference was seen in ORR or PFS between non-obese and obese patients. The study was underpowered to perform tests of statistical significance by race. These data preliminarily suggest pembrolizumab may not need to be adjusted for weight. Larger scale multi-institution trials with a particular emphasis on the recruitment of non-Hispanic Black patients can help clarify whether race-based differences in dosing pembrolizumab may be needed. [Table: see text]