In line with a previous prospective study are the results of a retrospective observational study of a total of 66 HER2+ breast cancer patients showing high levels of NT-proBNP (OR = 22.0, 95% CI (5.7–85.4); p < 0.0001) in patients who experienced cardiotoxicity during trastuzumab therapy (18 out of 66 patients, 27.3%) with a strong association with diabetes mellitus (OR = 5.9, 95% CI [1.2–28.5]; p = 0.028) as revealed by a binary logistic regression analysis [123]. Here, ERBB2 is linked to breast cancer.