Abstract P5-11-03: Practice patterns and outcomes of post progression treatment after CDK 4/6 inhibitors

Abstract

Abstract Background: CDK 4/6 inhibitors have become frontline treatment for patients (pts) with advanced hormone receptor (HR) positive breast cancer. There is limited data regarding post-progression outcomes in pts receiving CDK 4/6 inhibitors as standard of care. In this study, we analyzed treatment patterns and clinical outcomes of post-progression treatment in pts with advanced HR positive breast cancer after receiving CDK 4/6 inhibitors. Methods: Pts with metastatic breast cancer receiving CDK 4/6 inhibitors who received treatment after progression were identified from a cohort of pts at MDACC. Pts receiving CDK 4/6 inhibitors in a clinical trial were excluded. Clinical and demographic data as well as progression-free survival (PFS) was collected. Data was analyzed using Fischer's exact test for categorized variables and T test/Wilcoxon rank-sum test for continuous variables. PFS was analyzed using the Kaplan Meier method. Results: 206 pts who met eligibility criteria were included. Median age at metastatic diagnosis was 56 years-old and the majority of pts were white (n=160, 77.7%) with a pre- treatment performance status of 0 (n=168, 81.6%). The largest fraction of pts (n=98, 47.6%) received a chemotherapy agent following progression on a CDK 4/6 inhibitor while 19.4% (n=40) received endocrine therapy, 21.8% (n=45) received a biologic, 6.3% (N=13) received a different CDK 4/6 inhibitor and 4.9% (n=10) received an investigational therapy. The majority of pts who progressed on a subsequent agent had visceral progression (n=193, 93.7%). The median time to progression on an agent after CDK 4/6 inhibitor was 122 days. There was no statically significant difference in time to progression after CDK 4/6 inhibitor between pts receiving different classes of therapies, including CDK 4/6 inhibitors and investigational therapies (p=0.3). Conclusion: Pts in our cohort were more likely to receive chemotherapy following progression on a CDK 4/6 inhibitor. Reassuringly, there was no significant difference between time to progression on different agents. As CDK 4/6 inhibitors become frontline therapy for HR positive metastatic breast cancer, it is important to evaluate the sequencing of therapies as well as outcomes on subsequent agents. Citation Format: Katherine Keaney Clifton, Akshara Singareeka Raghavendra, Min Yi, Jennifer Litton, Debu Tripathy, Meghan Karuturi. Practice patterns and outcomes of post progression treatment after CDK 4/6 inhibitors [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-11-03.