Retrospective Cohort Study of CDK4/6-inhibitor-induced Alopecia in Breast Cancer Patients.

e13083 Background: The synergistic effects of novel combined cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) and endocrine therapy has increased their utilization for treatment of metastatic breast cancer. When compared to endocrine monotherapy, CDK4/6i may increase the risk of alopecia by nearly two-fold (Eiger D, et al. PMID: 32167397; Chan D, et al. J Clin Oncol.). The prevalence of this adverse effect underscores the importance of characterizing CDK4/6i-induced alopecia (CDKIA) and investigating therapeutic options. Methods: A retrospective cohort of 28 female patients with breast cancer and endocrine-induced alopecia (EIA) or CDKIA. Onset of alopecia was measured by time (months) between initiation of anticancer therapy and dermatology referral. Therapeutic response to minoxidil (LDOM or topical [5%] solution or foam) was assessed by both Dean Scale and qualitative clinical improvement by comparison of pre-treatment and post-treatment clinical images by 2 board certified academic dermatologists (ST and BD). Results: Androgenetic alopecia was the most common hair loss distribution (n=27, 96.4%), with CDKIA patients having preferential vertex involvement (n=7 [70.0%] CDKIA vs. n=4 [36.4%] EIA; p=0.04). Patients on CDK4/6i had shorter times to dermatology referral (mean time [months]: 44.6±37.1 for EIA vs. 9.4±13.7 CDKIA; p=0.003). After 16-24 weeks of minoxidil, moderate to significant improvement of alopecia occurred in 80% of CDKIA patients versus 94.4% of EIA patients. Despite similar baseline alopecia grade severity, significant improvement was only observed in EIA patients (mean pretreatment Dean Score – post-treatment Dean Score: -0.44; p=0.0002). Conclusions: Compared to EIA, the onset of CDKIA happened more rapidly and was more resistant to minoxidil. The preferential vertex involvement observed among patients with CDKIA may suggest combination therapy with topical or oral minoxidil and topical anti-androgens may lead to more favorable outcomes. Prompt dermatology referral should be considered for patients treated with CDK4/6i + ET. [Table: see text]