Presentation (CTI)

OBJECTIVES: This retrospective study used US claims data to develop a treatment-based proxy to identify patients with HR+ HER2- metastatic breast cancer (mBC) and evaluated the performance of the proxy using biomarker data in electronic medical records (EMR).
METHODS: Between 03/2019-11/2022, patients with ≥1 ICD-10 diagnosis code for BC and metastasis were identified in IQVIA PharMetrics® Plus database. Patients with continuous enrollment 6 months prior to (baseline) and ≥3 months after (follow-up) the index date (earliest metastasis code), and no diagnosis codes for other cancers or metastasis within 15 months pre-index were included. A treatment-based proxy was used to ascertain HR+ HER2- status where patients with: 1) endocrine therapy or targeted therapies indicated for HR+ HER2- mBC (CDK4/6, mTOR, PIK3CA inhibitors) and 2) no HER2+ or triple-negative mBC treatment during follow-up were included. Patients were further linked to the IQVIA Oncology EMR database for HR and HER2 status based on biomarker testing.
RESULTS: Out of the 19,117 mBC patients identified in claims, 11,419 (59.7%) patients had ≥1 line of therapy and were defined as HR+ HER2- using the treatment-based proxy. Of these, 392 patients (3.4%) were linkable to Oncology EMR and 154 linked patients (39.3%) had non-missing HR and HER2 biomarker data. The positive predictive value of the treatment-based proxy was 100% for HR+ status and 95.5% for HER2- status. The 4.5% of patients (n=7) with misclassified HER2 status (i.e., with HR+ HER2+ in OncEMR) had claims for endocrine therapy and chemotherapy and no evidence of targeted therapy during follow-up period.
CONCLUSIONS: Treatment-based proxies are often used in claims database studies to identify patients with specific subtypes of breast cancer when biomarker data are not available. Our treatment-based proxy can be used to reliably identify patients with HR+ HER2- mBC and subsequently evaluate clinical and economic outcomes.