OBJECTIVES: Anti-HER2 therapies have significantly improved survival in human epidermal growth factor 2 (HER2)-positive metastatic breast cancer (mBC). However, clinical trials have identified increased cardiac risk with trastuzumab-based therapies. The purpose of our study was to assess the incidence of cardiac safety events after trastuzumab initiation among elderly HER2+ mBC patients in the real-world setting.

METHODS: We identified 73 eligible HER2+/ hormone receptor-negative mBC patients diagnosed between February 2013 and December 2015 (mean age at diagnosis, 75.0±7.7 years) from SEER and followed their MEDICARE records through December 2016. Fifty-six patients were treated with trastuzumab, and among them, five received ado-trastuzumab emtansine (T-DM1) as second-line therapy during the study period. We identified the occurrence of cardiac safety events 12 months before diagnosis through patient death or the end of observation. We defined a cardiac safety event as inpatient or outpatient cardiomyopathy (CM) or heart failure (HF).

RESULTS: There were no significant baseline differences between patients treated with trastuzumab or not, except that the non-trastuzumab group had a higher proportion of patients with a prior history of CM/HF. Eight of the 56 patients (14.3%) developed CM/HF during or following trastuzumab treatment, including one HF hospitalization. Three of the 8 patients (37.5%) who developed CM/HF had pre-existing cardiac conditions. Four of the 8 patients (50%) died within one month of developing CM/HF. The average number of cardiac events per trastuzumab-treated patient was 2.9. Excluding patients with a history of CM/HF before mBC diagnosis, the incidence of CM/HF was 9.6% in patients treated with trastuzumab and 6.7% in patients without trastuzumab treatment (OR, 1.49; 95%CI, 0.16-13.83).

CONCLUSIONS: Our results suggest that elderly patients treated with trastuzumab-based therapies do not have an increased cardiac safety risk compared with patients with no trastuzumab-based treatment. However, our results are limited by the small size of our cohort.