The potential benefit of trastuzumab-based therapy upon lapatinib progression in heavily preatreated patients with advanced HER2 positive breast cancer.

e11576 Background: Overexpression of human epidermal growth factor receptor 2 (HER2) occurring in about 20% of breast cancers is associated with increased risk of disease recurrence and worse prognosis. Despite the advent of therapies that target HER2, particularly, trastuzumab and lapatinib, that have altered the natural course of HER2-positive advanced breast cancer, tumor progression remains inevitable. New agents are in clinical development, but up to date there are limited data to direct the treatment of patients after lapatinib progression. Methods: We retrospectively searched for HER2-positive advanced breast cancer patients treated at our clinic, who received both trastuzumab-based therapy and lapatinib upon trastuzumab-progression in the metastatic setting. Thirty patients, all female, suffering from HER2-positive advanced breast cancer were identified. HER-2 positivity was assessed by immunohistochemistry (IHC 3+) or chromogenic in situ hybridization (CISH+). Results: Of the 30 patients, 83.3% had invasive ductal carcinoma; 60% had positive hormone receptor status, and 80% grade 3 tumours. Half of the patients received adjuvant trastuzumab. Median age was 57 years, range 37-79 years. 36.6% were switched to lapatinib after a median of three (range 2-6 lines) trastuzumab-based treatment lines. In 8 pts (37.5%) trastuzumab was re-started after lapatinib progression. In 7 of these patients, trastuzumab was combined with chemotherapy. Median progression free survival and overall survival in these patients was 4.75 and 8.87 months respectively. 3 patients received bevacizumab-based therapy upon lapatinib failure. Conclusions: Trastuzumab rechallenge after lapatinib progression may be active in a subgroup of heavily pre-treated patients. Clinical benefit of this strategy has to be balanced especially in limited resource settings with unavailability of novel agents or early phase clinical trials. As of now, there is no uniform accepted standard to define the optimal treatment approach of patients upon lapatinib progression showing the real need for new therapies in this population.