Treatment patterns and survival in metastatic breast cancer patients by tumor characteristics

Objectives: Study objectives were to compare the treatment patterns and clinical outcomes among metastatic breast cancer (mBC) patients by receipt of HER2-targeted agents and among subgroups of HER2-targeted agent users. Research design and methods: Adult women newly diagnosed with mBC (index date) during 2008-2012 were selected from the Truven MarketScan databases and followed until end of enrollment or inpatient death. Patients with<12 months of data, pre-index primary cancers other than breast cancer, pregnancy, or HIV/AIDS were excluded. Study cohorts were users and nonusers of HER2-targeted agents and women with no treatment; and HER2-targeted agent subgroups by receipt of hormonal therapy (HT), de novo vs. recurrent status, and age group. Pre-and post-index breast cancer treatments were compared across cohorts. Relative risk of progression and death were evaluated among the subset of patients with mortality data. Results: Of 18,059 eligible women selected, 14.6% were users of HER2-targeted agents, 71.1% were nonusers, and 14.3% untreated. HER2-targeted agent users received more aggressive cancer treatments compared to nonusers. HER2-targeted agent users were 33% more likely to progress and had a similar risk of death compared to nonusers. Among HER2-targeted agent subgroups, the risk of progression was 30% lower among HT+ patients vs. HT-, 32% lower for de novo vs. recurrent, and similar across age groups. The risk of death was 52% lower for HT+ vs. HT-, 35% lower for de novo vs. recurrent, and increased with age. Limitations: Identification of distant metastasis, tumor receptor expression and disease progression were based on claims data rather than on clinical assessment. Conclusions: Receipt of HER2-targeted agents (vs. non-HER2-targeted agents) was significantly associated with receipt of pre-and post-index breast cancer treatments. HER2-targeted agent users were more likely to progress but had a similar risk of death during follow-up. Among HER2-targeted agent subgroups, HT+ and de novo status were associated with a reduced risk of progression and death.