Retreatment with trastuzumab-based therapy after disease progression following lapatinib in HER2-positive metastatic breast cancer

Background: Preclinical data suggest that treatment with lapatinib reinduces sensitivity to trastuzumab in human epidermal growth factor receptor 2(HER2)-positive breast cancer cells. Patients and methods: Between January 2007 and November 2010, 179 HER2-positive metastatic breast cancer patients were treated with lapatinib and capecitabine at nine Italian institutions. We evaluated the clinical outcome of 69 patients (38.5%) retreated with trastuzumab after lapatinib progression. Results: Visceral metastases were identified in 51 (74%) and brain metastases in 16 patients (23%). All patients were pretreated with both trastuzumab- and lapatinib-based therapy. We observed with retreatment with trastuzumab-based therapy: 1 complete remission (2%), 18 partial remission (29%) and 10 stable disease ≥6 months (14%) and 47% of clinical benefit (CB). Median duration of response was 8.1 months [95% confidence interval (CI) 5.5-10.7]. No unexpected toxic effects occurred. At a median follow-up of 13 months, median progression-free survival was 4.9 months (95% CI 4.2-5.6) and overall survival (OS) 19.4 months (95% CI 14.0-25.0). Median OS was longer for patients experiencing CB (not reached versus 13.4 months for patients without CB, P = 0.002). Brain involvement was associated with lower median OS (17.3 versus 23.3 months for patients without brain disease; P = 0.021). Conclusion: Retreatment with trastuzumab-based therapy showed CB in 47% of patients progressing during lapatinib-based therapy, leading to a prolonged OS.