Comparison of treatment patterns and outcomes in metastatic breast cancer (MBC) patients initiated on trastuzumab versus lapatinib: A retrospective analysis.

Abstract

e11076 Background: The National Comprehensive Cancer Network (NCCN) guidelines recommend trastuzumab- or lapatinib-based therapies as the preferred agents for metastatic HER2-positive breast cancer. Few studies have compared treatment patterns and outcomes in MBC patients (pts) treated with trastuzumab vs. lapatinib. The objective of this study is to compare rates of new metastatic sites, discontinuation, healthcare resource utilization, and costs in MBC pts initiated on lapatinib vs trastuzumab. Methods: Adult women with MBC initiated on trastuzumab or lapatinib on or after 03/13/2007 (lapatinib FDA-approval date) were selected in the PharMetrics® Integrated Database (2000-2011). Pts were followed from trastuzumab or lapatinib initiation date up to the end of continuous healthcare plan enrollment/data availability, whichever occurred first. New metastatic sites and discontinuation rates (gap ≥45 consecutive days) were compared among trastuzumab and lapatinib pts using multivariate Cox proportional-hazards models. Incremental healthcare resource utilization and monthly costs (2010 USD; measured from a payer perspective) were estimated using multivariate generalized linear models. Results: Among the643 pts selected, 381 and 262 pts were initiated on trastuzumab and lapatinib, respectively. After multivariate adjustment, compared to trastuzumab pts, lapatinib pts had a higher rate of new metastases (hazard ratio [HR]=1.65; p<.001) and treatment discontinuation (HR=1.57; p<.001). There was no statistically significant difference in total healthcare cost between lapatinib and trastuzumab pts (p=.397). The incidence of medical visits associated with treatment administration was lower in lapatinib pts (Incidence rate ratio [IRR]=0.34; p<.001), however, the incidence of other outpatient visits was significantly higher in lapatinib pts (IRR=1.19; p<.001). Conclusions: Whileboth cohorts presented similar healthcare costs, pts initiated on lapatinib showed higher rates of new metastatic sites, discontinuation, more outpatient visits (non treatment-related), but fewer medical visits associated with treatment administration.