Trastuzumab-induced cardiotoxicity (TIC) is the primary adverse event that 
limits the use of trastuzumab in HER2-positive breast cancer patients. However, 
the incidence and risk factors of TIC in HER2-positive gastric cancer are not 
known. Therefore, we evaluated the incidence and predictive factors of TIC in 
gastric cancer patients treated with trastuzumab in clinical practice. We 
reviewed cardiac dysfunction in HER2-positive gastric cancer patients between 
December 2005 and April 2015 in a prospectively-collected database that included 
prospective clinical trials at Yonsei Cancer Center, Republic of Korea. TIC was 
defined as an absolute decline in left ventricular ejection fraction (LVEF) of 
at least 10 percentage points from the baseline to a value less than 55%, as 
identified by a multiple-gated acquisition scan or an echocardiogram. Among the 
115 patients, 70 patients (60.9%) received trastuzumab combined with 
chemotherapy, and 45 patients (39.1%) received chemotherapy alone as a 
first-line therapy. Symptomatic heart failure was not observed in either group, 
but a significant asymptomatic drop in LVEF was noted in five (7.1%) of the 
trastuzumab combined-group patients and in one (2.2%) chemotherapy-only group 
patient [hazard ratio (HR), 3.47; 95% confidence interval (CI), 0.40-29.8; 
P=0.257]. TIC was observed more frequently in elderly patients than in younger 
patients (HR, per age in year, 1.16; 95% CI, 1.02-1.31; P=0.019). Similar to 
prior observations in breast cancer, TIC in gastric cancer patients is not 
frequent or reversible. However, the asymptomatic drop in LVEF should be 
monitored continually in HER2-positive gastric cancer patients treated with 
trastuzumab, especially in elderly patients.