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

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.

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.

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.

Identification of distant metastasis, tumor receptor expression and disease progression were based on claims data rather than on clinical assessment.

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.