When used in combination with myelosuppressive chemotherapy, trastuzumab may increase incidence of neutropenia (moderate-to-severe) and febrile neutropenia. Infusion reactions (including fatalities) associated with use. Trastuzumab is associated with symptomatic and asymptomatic reductions in left ventricular ejection fraction and severe heart failure and may result in mural thrombus formation and stroke, and even cardiac death (extreme caution should be used in pre-existing cardiac disease or dysfunction). Concomitant administration of anthracyclines and prior exposure to anthracyclines or radiation therapy significantly increases risk of cardiomyopathy. Trastuzumab also associated with arrhythmias and hypertension. May cause serious pulmonary toxicity (dyspnea, hypoxia, interstitial pneumonitis, pulmonary infiltrates, pleural effusion, noncardiogenic pulmonary edema, pulmonary insufficiency, acute respiratory distress syndrome, and/or pulmonary fibrosis). Use caution in pre-existing pulmonary disease or extensive pulmonary tumor involvement (may have more severe toxicity).