Introduction: Trastuzumab is a humanized anti-HER2 monoclonal antibody, which is used for the immunotherapy of breast cancer. The most frequent manifestation of trastuzumab-induced cardiotoxicity is a reversible decrease in left ventricular contractility, without myocardial necrosis. It is quite often (occurs in 5 to 10% of patients) and in most cases, after the cessation of therapy, recovery of systolic function can be achieved. Rarely, there can be a progression to irreversible dilated cardiomyopathy. (1-3)

Case report: A 55-year-old female patient with the breast carcinoma (T1N2MO, HER-2 positive) was done a segmentectomy of the left breast. After chemotherapy (ACx6) and radiotherapy (50 Gy), it was planned to start the immunotherapy with trastuzumab during 1 year in 3-week cycles. After the 4th cycle of trastuzumab, the patient started to feel weakness and dyspnea during a light physical activity. An echocardiographic examination showed a decrease of LVEF on 25%, significant mitral and tricuspid valve regurgitation and the high blood pressure in pulmonary artery. The treatment with trastuzumab was stopped. Therapy with ACE-inhibitor, beta-blocker and diuretic was started, what caused a gradual improvement of EF on 40% and reduction of MR and TR. Six years later the patient was admitted to University Hospital Centre Rijeka with symptomatic sustained ventricular tachycardia. Echocardiographic examination showed deterioration of LVEF on 25 to 30%. Coronarography was also done and it showed no pathology of coronary arteries. The patient was implanted a permanent cardioverter defibrillator. The further episodes of VT were not registered. Because of frequent paroxysms of atrial fibrillation, amiodarone and anticoagulant therapy were started. The patient is under regular controls of cardiologist and oncologist and has no signs of recidive of the cancer at the moment.

Conclusion: In most cases trastuzumab-induced cardiotoxicity is reversible, but there is a small number of patients who develop irreversible dilated cardiomyopathy with all complications of that disease, including malignant ventricular arrhythmias. By timely and adequate treatment, it is possible to prolong the life and to improve the quality of life in that group of patients.