Toxicity differences in CDK 4/6 inhibitors seen in Asian and Pacific Islanders.

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e13086 Background: Cyclin-dependent kinases (CDK) 4/6 inhibitors are the standard of care, first line treatment for hormone receptor positive metastatic breast cancer and adjuvant high-risk hormone receptor positive early stage breast cancer along with endocrine therapy. There have been multiple clinical trials validating the effectiveness, along with toxicities of these agents; however, the majority of these trials lack ethnic diversity. This shortcoming limits the ability to apply these findings in diverse patient populations, especially among Asian and Pacific Islanders in Hawaii. Objective: To determine if the toxicity profile of CDK 4/6 inhibitors in women with breast cancer is different among patients at a community oncology practice in Hawaii, in which the majority of patients are Asian, Pacific Islander or a combination of both when compared to three landmark trials. Methods: A retrospective analysis of thirty-two patients with hormone receptor positive, HER2 negative metastatic or high risk breast cancer who started endocrine therapy and CDK 4/6 inhibitor therapy (abemaciclib, ribociclib, or palbociclib) between 2018-2023. Graded toxicities of each individual patient based on CTCAE criteria V. 5, along with demographic data was reviewed and compared to three main registration trials for these agents (MONARCH-3, MONALEESA-2, PALOMA-2). Results: Combined results from the three large randomized trials reported an average of 75% of participants were Caucasian, as compared to 15% in the Hawaii data. While 19% percent of participants from the combined large randomized trials reported being of Asian descent, none of these trials reported a breakdown of Asians versus Pacific Islanders. In the Hawaii sample, 41% were reported as Pacific Islander and 41% reported as Asian, 15% Caucasian, with the final 3% reported as Hispanic. Collective analysis of the FDA registration trials contained 0% Pacific Islander, 19.8% Asian, 74.3% White, 1.5% Black, and 4.4% Other. The majority of all toxicities of all grades were higher in the Hawaii population as compared to the three national trials, except for neutropenia with ribociclib and diarrhea with palbociclib (Table). Conclusions: The Hawaii analysis that was primarily comprised of Asians and Pacific Islanders revealed an increased incidence of toxicities, despite starting at lower doses rates for all CDK 4/6 inhibitors. This data analysis begins to highlight the importance of representative populations in clinical trials for the most effective and safest care of diverse populations. [Table: see text]