Abstract P3-23-05: Evaluation of CDK 4/6 inhibitor practice patterns and institutional versus national adherence to palbociclib laboratory monitoring in breast cancer patients

Abstract Background: Cyclin dependent kinase (CDK) 4/6 inhibitors (CDK 4/6i) can improve outcomes in ER-positive/HER2-negative (ER+/HER2-) breast cancer. The choice of CDK 4/6i selection and dose depends on clinical context and/or potential side effect of profile of each unique CDK 4/6i. The objective of this study was to evaluate practice patterns in patients initiated on CDK 4/6i and assess adherence to recommended laboratory monitoring in breast cancer patients in both an institutional and national dataset. Methods: The institutional cohort (IC) involved a retrospective chart review of patients newly initiated on palbociclib between May 8, 2018 - June 4, 2019 at Mayo Clinic, Rochester. The national cohort (NC) reviewed medical and pharmacy claims data from the OptumLabs Data Warehouse (OLDW) and included patients who were initiated on palbociclib (P), ribociclib (R) or abemaciclib (A) between February 6, 2015 - September 30, 2019. NC patients were required to have a minimum of 6 months baseline coverage, 6 months coverage after first prescription and Day 1 labs drawn. For both cohorts, patients were ≥18 years old with metastatic ER+/HER2- breast cancer. Data was collected for up to 6 cycles of treatment and included cycle start dates, doses, dates of lab draws and dose changes. Laboratory adherence was defined as a complete blood count being drawn +/- 3 days of the defined timepoint for the IC and +/- 5 days for the NC with a l4-day window for Cycle 1, Day 1 labs. Results: The IC included 81 patients and the NC 2600. In the NC, the most prescribed CDK 4/6i was P (90%), followed by A (6%) and R (4%). Prescription breakdown by geographic region was Midwest (26%), Northeast (14%), South (47%), West (13%). Ethnic breakdown of the group was White (68%), Black (15%), Hispanic (8%), Asian (3%) and unknown (6%). P practice pattern data were available for both the IC and NC, but R and A data in the NC only. In the IC, the initial P dose was 125 mg (95%), 100 mg (1%) and 75 mg (4%). In the NC, P (n=2329) dose was 125 mg (81%), 100 mg (15%) and 75 mg (4%). Dose reductions were common with 25% and 28% of patients requiring one dose reduction and 16% and 9% of patients requiring two dose reductions in the IC and NC, respectively. In NC patients initially treated with P, 5% were subsequently treated with A and 2% with R. In the NC, A (n=163) was initiated at 200 mg (7%), 150 mg (79%), 100 mg (10%) and 50 mg (4%). One dose reduction was required in 25% of patients and 6% required two dose reductions. Of those initially treated with A, 16% were subsequently treated with P and 1% with R. In the NC, R (n=108) was initiated at 600 mg (81%), 400 mg (8%) and 200 mg (11%). One dose reduction was required in 17% of patients and 2% required two dose reductions. Of those initially treated with R, 7% each were subsequently treated with P and 10% with A. Laboratory adherence was assessed for P only. For the IC, a total of 81 patients were included (mean age 61±13 years, 98% female and 95% White). The NC included 2329 patients (mean age 66±12 years, 99% female and 69% White). Laboratory adherence is listed in the table below: Conclusions: P was the most commonly prescribed CDK 4/6i. Dose reductions were less common with R. Adherence to laboratory monitoring was higher in our institutional cohort than in a national administrative claims database. Initiatives to ensure that labs are drawn at recommended timepoints during P therapy will be important for safety. ICNCC1D193%100%C1D1589%61%C2D191%71%C2D1558%55%C3D199%62%C4D190%55%C5D184%53%C6D178%50%C = cycle, D = day. Citation Format: Jodi Taraba, Kavya Swarna, Allison Golbach, Lindsey Sangaralingham, Kathryn Ruddy, Kristin Mara, Matthew Smith, Tufia Haddad, Karthik Giridhar. Evaluation of CDK 4/6 inhibitor practice patterns and institutional versus national adherence to palbociclib laboratory monitoring in breast cancer patients [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 P3-23-05.