Abstract P1-19-03: Phase II trial of durvalumab and tremelimumab in the hormone receptor-positive metastatic breast cancer with high tumor mutational burden selected by whole exome sequencing: Korean cancer study group trial (KCSG BR17-04)

Abstract

Abstract Background: Hormone-receptor (HR) positive breast cancer is the main subtype of breast cancer. Although overall survival of HR-positive metastatic breast cancer (MBC) patients has improved by various therapies including endocrine therapies, CDK4/6 inhibitors, and cytotoxic chemotherapy, it is still considered incurable. Immune checkpoint inhibitors have rarely been clinically tested in HR-positive breast cancer, despite proving anti-cancer activity in early and metastatic triple-negative breast cancer in various trials. We evaluated efficacy and safety of combined durvalumab and tremelimumab in the HR-positive MBC, which was enriched with high tumor mutational burden (TMB). Methods: HR-positive MBC patients who received prior 1 or more lines of therapy in metastatic setting were prescreened with whole exome sequencing (WES) using metastatic or recurred tumor biopsies. Criterion of high TMB was defined as upper 30%. In the beginning, the criterion of high TMB was 2.1 mutations per Mb, based on the retrospective WES database in Yonsei Cancer Center and this criterion was recalculated every 30 cases. Patients who met upper 30% of TMB were treated with combined durvalumab (1500mg every 4 weeks upto 13 doses) and tremelimumab (75mg every 4 weeks upto 4 doses). Response was evaluated every 2 cycles using RECIST 1.1 and toxicity was evaluated using NCI-CTCAE 4.03. Tumor-infiltrating lymphocyte (TIL) and PD-L1 expression were also analyzed to investigate a correlation with TMB. Results: Biopsies of recurrent or metastatic tumors were taken from a total of 119 patients for WES assay. A median turn-around-time of TMB data was 30.0 days (range, 16~67). Of these 119 patients, a median number of nonsynonymous mutations was 2.0 per Mb (range, 0~21.7) with upper 30% criterion of 3.1. High TMB showed a trend toward old age (P=0.074) and single positivity of estrogen receptor (ER) or progesterone receptor (PR) compared to positivity of both ER and PR (P=0.055). TMB was positively correlated with TILs (r=0.289, P=0.005). Thirty patients with high TMB received study treatment with a median 2 cycles (range, 1~13). A median prior lines of therapies in metastatic setting was 4 (range, 1~9). The objective response and clinical benefit rates were 6.3% (2 PRs of 30) and 20% (2 PRs plus 4 SDs of 30). There was one treatment-related mortality due to pneumonitis. Immune-related adverse events included endocrinopathy (n=3; hypothyroidism in 2, hyperthyroidism in 1), enteritis (n=2), skin rash (n=2), pneumonitis (n=1), and so on. Biomarker analyses are underway. Conclusions: WES-based TMB using metastatic tumor biopsy was a feasible platform to prescreen HR-positive MBC patients. Combined durvalumab and tremelimumab showed a modest activity and good tolerability in heavily treated, HR-positive MBC with high TMB. Citation Format: Yong Wha Moon, Eunyoung Kim, Min Hwan Kim, Gun Min Kim, Seul-Gi Kim, YeeSoo Chae, Jieun Lee, Jae Ho Jeong, Kyung-Hun Lee, Han Jo Kim, Joo Young Jung, Su-Jin Koh, Kyoung Eun Lee, Hee-Jun Kim, Kyong Hwa Park, Seungtaek Lim, Yeon Hee Park, Tae Hoen Kim, Sewha Kim, Yohan Yang, Sangwoo Kim, Joohyuk Sohn. Phase II trial of durvalumab and tremelimumab in the hormone receptor-positive metastatic breast cancer with high tumor mutational burden selected by whole exome sequencing: Korean cancer study group trial (KCSG BR17-04) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-19-03.