Factors impacting treatment with a CDK4/6i in first line metastatic HR+/HER2- breast cancer patients.

e13079 Background: The inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i), abemaciclib, palbociclib and ribociclib, are indicated for the treatment of metastatic breast cancer (mBC) patients (pts) with hormone receptor positive (HR+), human epidermal growth factor receptor-2 negative (HER2-) disease. This real-world study sought to understand the factors for whether pts receive or do not receive a CDK4/6i among those eligible in the first line (LOT 1) treatment of mBC. Methods: A retrospective, observational analysis of data from pts in the IntegraConnect PrecisionQ real-world de-identified database. The study included adults (age ≥18 years) with HR+/HER2- mBC who initiated LOT 1 treatment between January 1, 2020 and December 31, 2024. Pts with a second primary cancer were excluded. Pts were assessed to see whether age of pt at time of treatment, race, eastern cooperative group (ECOG) status, site of metastatic disease, de-novo vs. recurrent disease, or volume of pts treated by a provider impacted treatment with a CDK4/6i +/- endocrine therapy. Data are presented using descriptive statistics and comparisons were performed using chi-squared analyses. Results: Of the 4532 pts with HR+/HER2- mBC who initiated LOT 1 therapy included in the analysis, most were female (98.6%), most were white (64.1%), and the median age at LOT 1 treatment was 67 [IQR 57, 76]. Among eligible pts, 70.7% received a CDK4/6i. The use of CDK4/6i by age was as follows: 61.7% among pts who were <45 years of age (N = 379), 72.4% among pts 46 to 85 years of age (N = 3880), and 59.5% among pts > 85 years of age (N = 273) (p < 0.01). The use of CDK4/6i by race was as follows: 71.6% among White (N = 2906), 67.9% among Black/African American (N = 386), 64.2% among Asian (N = 81), and 70.1% among all Other (N = 1159) (p > 0.05). The use of CDK4/6i by ECOG was as follows: 73.5% among ECOG 0 (N = 1439), 69.7% among ECOG 1 (N = 1247), 71.1% among ECOG 2 (N = 356), 58.9% among ECOG 3 (N = 107), 57.1% among ECOG 4 (N = 14), and 69.8% among ECOG unknown (N = 1369) (p < 0.01). The use of CDK4/6i based on metastatic sties was as follows: 75.0% among bone-only (N = 2623), 76.2% among bone and either lung, liver or brain (N = 432), 63.5% among either lung, liver or brain, but no bone (N = 900), and 58.6% among unknown sites (N = 577) (p < 0.01). Among pts with who were stage IV at diagnosis (N = 1872) 70.6% received a CDK4/6i whereas pts who had a recurrence (N = 2652) 70.6% received a CDK4/6i. Among 375 providers who saw < 5 pts (N = 795) 65.0% prescribed a CDK4/6i, among 194 providers who saw 5-10 pts (N = 1345) 70.9% prescribed a CDK4/6i, and among 144 providers who saw > 10 pts (N = 2392) 72.6% prescribed a CDK4/6i (p < 0.01). Conclusions: Pts with HR+/HER2- mBC who initiated LOT 1 therapy were more likely to receive a CDK4/6i if they were between the age of 46 and 85, had metastasis to the bone, had a better performance status (ECOG < 2), or were treated by a provider who saw more > 5 HR+/HER2- mBC pts who initiated LOT 1.