Real-World Practice Patterns in Diagnosis and First-Line Treatment in Metastatic Breast Cancer

Divergence from national guidelines and variations in practice patterns impact care and outcomes in patients with metastatic breast cancer (MBC). We sought to assess the quality of care in the diagnosis and treatment of real-world patients with MBC in Washington State.

Data were retrospectively analyzed using a linked cancer registry and insurance claims platform for patients with recurrent or de novo MBC diagnosed between 2008 and 2019.

We identified 1101 patients with MBC (median age: 66), 715 recurrent and 386 de novo. Most patients were White (89%), all were insured (Commercial [47%], Medicaid [4%], Medicare [35%], or multiple [13%]), and 15% lived in areas of high deprivation (Area Deprivation Index [ADI]: 8-10). Of the patients with recurrent MBC, less than half received a biopsy (49.5%) or biomarker reassessment (48.7%) to confirm the diagnosis of MBC. Patients treated at high- and medium-volume centers had higher rates of biopsy than low-volume clinics (51.9%, 54.3%, and 40.7%, respectively, p = 0.03). ET alone was more common in patients who did not undergo biopsy (62.3% vs. 37.7%, p < 0.001) or biomarker reassessment (62.7% vs. 37.3%, p < 0.001). Among the 677 patients with estrogen receptor (ER)+/HER2- MBC (de novo and recurrent), most received ET alone (69%), followed by CT (22%) and CDKi + ET (9%). Importantly, 40% of patients were treated before CDK4/6i approval. Most patients who received CDKi + ET were < 65 years old (65.2%, p < 0.02). Patients with commercial insurance were more likely to receive CDKi + ET compared to those with Medicare/Medicaid. (60.9% vs. 26.1%, p = 0.10).

Our findings highlight key gaps in MBC management and serve as a launch point for patient-centered and quality-promoting initiatives.