Abstract P2-26-07: Alteration of gut microbiota signatures and its association with diarrhea during abemaciclib treatment: A multicenter prospective cohort study (KBCRN-A002 study)

Abstract Background: Abemaciclib is a selective CDK4 and CDK6 inhibitor with demonstrated efficacy in hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer. The most common adverse event across previous trials was early-onset diarrhea, affecting the patients’ quality of life and necessitating dose reductions. However, the exact mechanism for the lower rate of diarrhea in the other CDK4 and CDK6 inhibitors compared with abemaciclib is unknown. Ample evidence indicates that the gut microbiome is a tumor-extrinsic factor associated with the anti-tumor response; however, reported microbial signatures associated with adverse events by anti-cancer agent are inconsistent. To determine the underlying mechanism, we evaluated the correlation between diarrhea with abemaciclib and microbiota signatures in a metastatic breast cancer cohort. Methods: The KBCRN-A002 study is a multicenter, prospective cohort study, which aims to evaluate the association between gut microbiota signatures and abemaciclib-induced diarrhea in breast cancer patients. Patients with metastatic breast cancer who were receiving abemaciclib were eligible. The primary objective of this study is the correlation between diarrhea and the microbiota signatures and immune profile. Incidence and severity of diarrhea were evaluated by the Bristol stool scale at baseline, from day 1 to day 14, and at day 90 of treatment. Stool samples were collected at baseline and at day 90 after the start of abemaciclib treatment. The gut microbiota signature was evaluated by 16S rRNA analysis. Blood samples were collected at baseline and at days 14 and 90 after starting abemaciclib to evaluate the correlation between the gut microbiota signatures and the systemic immune profile in peripheral blood mononuclear cells (PBMCs). The immune profile was evaluated by mass cytometry, multi-plex cytokines assay, and RNA-sequencing of bulk PBMCs. We characterized the gut microbiota signatures, immune cell composition, immune cell signature, comprehensive cytokines, and severity of diarrhea in all patients. Results: We analyzed 39 patients, 77 stool samples, and 117 blood samples. In the preplanned interim analysis, among the 39 patients, 90% experienced diarrhea. Depleted gut microbiome α-diversity was positively associated with abemaciclib treatment and the severity of diarrhea. The relative abundances of 10 intestinal bacteria species increased and those of 18 intestinal bacteria decreased significantly after abemaciclib treatment, including bacteria known to be involved in diarrhea severity and anti-tumor immunity, such as Faecalibacterium (Table). The immune cell and cytokine profiles in PBMCs were also associated with the gut microbiota signatures. Conclusions: Gut microbiota signatures are associated with abemaciclib-induced diarrhea and the immune profile in metastatic breast cancer patients. These findings can help to elucidate the mechanism of diarrhea caused by abemaciclib and offer strategies for its management and prevention. Intestinal Microbiota Altered by Abemaciclib Citation Format: Kosuke Kawaguchi, Yurina Maeshima, Hiroshi Ishiguro, Kazuhiko Yamagami, Sachiko Takahara, Hirofumi Suwa, Masae Torii, Shigenori Nagai, Yasuaki Sagara, Wakako Tsuji, Hiroyasu Yamashiro, Takeshi Kotake, Shinji Fukuda, Kuniaki Saito, Yasuko Yamamoto, Masako Kataoka, Yuki Himoto, Atsushi Yonezawa, Yukiko Fukui, Yuki Nakamura, Wei Li, Sunao Tanaka, Satoshi Morita, Masakazu Toi. Alteration of gut microbiota signatures and its association with diarrhea during abemaciclib treatment: A multicenter prospective cohort study (KBCRN-A002 study) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-26-07.