Effectiveness of trastuzumab in first-line HER2+ metastatic breast cancer after failure in adjuvant setting: A controlled cohort study.

e11571 Background: The evidence supporting the use of trastuzumab (T) in metastatic setting comes from studies that included (almost) only patients who never received prior T. We investigated the effectiveness of T as first line therapy for metastatic breast cancer (mBC) in women already treated with T in the adjuvant setting. Methods: Using record linkage of 4 admistrative healthcare databases of Lombardy, Italy, we identified 2046 women treated with T for early BC in 2006-2009, 96 of whom developed a metastasis and were retreated with T in first line for mBC (treatment group). We compared overall survival (OS) of these women with that of 197 women treated with T in first line for mBC, who were treated with therapies other than T for early disease (control group). We computed Kaplan-Meier 2-year OS, and used a proportional hazard model to estimate the hazard ratio (HR) of death of the intervention group as compared to the control group. Results: Two-year OS was 60.0% in the treatment group and 59.5% in the control group. The HR of death of the treatment group compared to the control group, adjusted by age and metastatic site, was 0.80 (95% Confidence Interval 0.50-1.28). Conclusions: Given the unavailability of data from randomized clinical trials, our data provide suggestive evidence that the outcome of women receiving first line T treatment for mBC after T-failure in adjuvant setting is comparable to that of women not exposed to T for early BC.