Prolonged survival of patients receiving trastuzumab beyond disease progression for HER2 overexpressing metastatic breast cancer (MBC).

BACKGROUND The aim of this retrospective analysis was to evaluate the impact of trastuzumab-based regimens on the survival of patients with HER2-overexpressing metastatic breast cancer (MBC). The study specifically focussed on the influence of the continuation of trastuzumab-based treatment despite tumor progression on survival. PATIENTS AND METHODS Patients with HER2 overexpressing MBC were included in this retrospective analysis. HER2 overexpression was determined by the immunohistochemical staining score (DAKO Hercep Test). Trastuzumab was applied at a loading dose of 4 mg/kg and a maintenance dose of 2 mg/kg. RESULTS Among 136 HER2 overexpressing patients (DAKO score 3+), 66 patients received first-line trastuzumab, 47 patients received trastuzumab as second-line therapy and 23 patients received trastuzumab beyond disease progression. There was no significant difference regarding the duration of trastuzumab-based treatment (first-line: 29.5 weeks vs. second-line: 25 weeks). Moreover, there was no difference in the response rate (first-line: 37.9% vs. second-line: 35.7%) or the median survival (p = 0.47 log rank). Patients who received = 2 trastuzumab-based regimens for MBC survived significantly longer compared to those who had received only 1 regimen (= 2 regimens: 62.4 months vs. 1 regimen: 38.5 months; p = 0.01 log rank). CONCLUSIONS Trastuzumab is highly effective in the treatment of HER2 overexpressing MBC. Compared to historical controls, overall survival appears to be markedly prolonged, particularly in patients who received sequential trastuzumab-based treatment beyond disease progression.