Second-Line Treatment of Her2-Positive Metastatic Breast Cancer: Trastuzumab beyond Progression or Lapatinib? A Population Based Cohort Study.

Background: The relative efficacy of lapatinib vs. continuing trastuzumab beyond progression (TBP) in HER2-positive metastatic breast cancer (MBC) patients, who progressed on first-line trastuzumab, is still unclear. The objective of this population based cohort study was to compare outcomes of lapatinib vs. TBP in daily practice.

Methods: All HER2-positive MBC patients who began second-line anti HER2 therapy between 1st January 2010 and 30th August 2013 were selected from Clalit Health Services' (CHS) electronic database. Available data on patient and disease characteristics and treatments were analyzed. The primary endpoint was overall survival (OS). Outcomes were compared using the Kaplan-Meier (log-rank) method and Cox proportional hazards model.

Results: 64 patients received second-line lapatinib and 93 TBP. The two treatment groups were similar in age and co-morbidity rates, but differed in proportion of prior adjuvant trastuzumab (lapatinib: 29.7%, TBP: 16.1%, P = 0.043) and rates of prior brain metastases (lapatinib: 32.8%, TBP: 10.8%, P = 0.01). Lapatinib median OS was 13.0 months (95% CI: 9.5-16.5) vs. 31.0 for TBP (95% CI: 20.6-41.4), P<0.001. On multivariate analysis, longer OS was preserved for TBP, after controlling for differences in age, adjuvant trastuzumab, duration of first-line trastuzumab therapy, brain metastases, visceral metastases and hormonal treatment [Hazard Ratio (HR) = 0.63, 95% CI: 0.40-0.99, P = 0.045].

Conclusion: In this comparative cohort study, OS of HER2-positive MBC patients treated with TBP was significantly longer than with lapatinib. These results might be especially relevant in settings where ado-trastuzumab-emtansine (TDM-1), the current preferred agent in this setting, is not available yet for patients.