Disparities in receipt of 1-st line CDK4/6 inhibitors with endocrine therapy for treatment of hormone receptor positive, HER2 negative metastatic breast cancer in the real-world setting.

Objective: This study used real-world observational data to compare profiles of patients receiving different first-line treatment for hormone receptor positive (ER+), HER2 negative, metastatic breast cancer (MBC): CDK4/6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) versus ET alone.

Method: From a nationwide electronic health record-derived Flatiron Health de-identified database including 280 US cancer clinics, we identified patients with hormone receptor positive, HER2 negative, metastatic breast cancer receiving 1st -line therapy with ET alone or CDK4/6i plus ET between February 2015 and November 2021. Patient sociodemographic status, MBC treatment regimen and outcomes were the focus of this analysis. Patient characteristics were compared using t-tests and chi-square tests. Logistic regression analysis was performed to examine the association of patient characteristics with the likelihood of receiving 1st -line CDK4/6i plus ET vs. ET alone. Kaplan-Meier method and Cox proportional hazards were used to test the impact of 1st -line treatment regimen on real-world progression-free survival (PFS) and overall survival (OS). Baseline characteristics were balanced using inverse probability weighting (IPW).

Results: The study population included 3,917 patients receiving CDK4/6i plus ET (n = 2170) and ET alone (n = 1747) for their MBC. Compared to patients receiving ET alone, those receiving CDK4/6i plus ET were younger (mean age 66.8 vs. 68.6, p < 0.001), more likely to present with de novo MBC (p < 0.001), had better performance status (50.2% vs. 40.5% patients with ECOG value 0, p = 0.001) and lower number of comorbidities (29.7% vs. 26.6% ≥ 1 comorbidity, p < 0.001). Logistic regression revealed increased odds of CDK4/6i plus ET in individuals aged 50-64 (OR: 3.42, 95% CI [2.41, 4.86]) and 65-74 (OR: 3.18, 95% CI [1.68, 6.02]) versus those aged 18-49 years of age. Black individuals had lower odds of CDK4/6i plus ET (OR: 0.76, 95% CI [0.58, 1.00]) compared to White individuals. Other characteristics associated with lower odds of CDK4/6i plus ET included patients with stage III disease (OR: 0.69, 95% CI [0.52, 0.92]), lower performance status (OR: 0.50, 95% CI [0.40, 0.62]), and Medicare insurance (OR: 0.73, 95% CI [0.30, 1.78]) compared to those with commercial and Medicaid insurance. After IPW adjustment, use of CDK4/6i plus ET as 1st -line treatment was associated with significantly longer median PFS compared to ET alone (27 vs. 17 months; hazard ratio [HR] = 0.61, p < 0.001). Median OS was 52 months in the CDK4/6i plus ET group and was 42 months with ET alone (HR = 0.74, p < 0.001).

Conclusion: In this real-world database, disparities in receiving 1st -line CDK4/6 inhibitors were seen by age, diagnosis stage, baseline performance status, comorbidity, and insurance status. In adjusted analysis, the use of 1st -line CDK4/6i plus ET yielded better PFS and OS rates than ET alone. Further efforts are essential to enhance equitable use of and access to this crucial drug class.