We found 681 trastuzumab metastatic breast cancer users in Lombardy in 2006–2009.
Thirty two (4.7%) women experienced severe cardiac adverse events.
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.
Predictors of worse OS were age, brain liver or lung metastasis, and chemotherapy.