Trastuzumab for HER2+ metastatic breast cancer in clinical practice: Cardiotoxicity and overall survival

The evidence on efficacy and safety of trastuzumab in metastatic breast cancers (MBC) mainly derives from randomized clinical trials. We assessed short- and long-term overall survival (OS) and cardiotoxicity in a large cohort of women with MBC treated with trastuzumab in clinical settings. Using healthcare administrative data of Lombardy (10 millions inhabitants), we identified a cohort of women receiving trastuzumab for MBC between 2006 and 2009. The cumulative risk of severe cardiac events and the OS from the first trastuzumab administration were estimated using the Kaplan-Meier method. Their predictors were assessed using Cox regression models. We found 681 trastuzumab MBC users. Thirty two (4.7%) women experienced severe cardiac adverse events. The cumulative risk increased sharply, reaching a value of 2.4% and 4.3% during the first and second year; thereafter it increased of about 1% per year. Age was a strong predictor of cardiotoxicity. The OS was 81.8%, 64.0%, 50.2%, 41.1% and 37.2% at 1, 2, 3, 4 and 5 years, respectively. Independent predictors of worse OS were: age, brain liver or lung metastasis compared to other metastasis, use of taxanes and other chemotherapies, a cardiac adverse event after trastuzumab use, and a higher time between metastasis and BC diagnoses. The incidence of cardiotoxicity among women treated with trastuzumab for HER2-positive MBC appeared higher than that reported in RCTs, particularly in elder patients. In spite of this, median survival, was, if anything, better.