Heart Muscle Cell Study for Breast Cancer Patients

Inclusion Criteria: * Female * Age greater than 18 years * Willing to participate in protocol procedures with signed informed consent * Assessment of LVEE via echocardiogram, cardiac MRI, or MUGA Subjects in the cardiotoxicity group (TOX) must meet the following criteria: * History of HER2 positive breast cancer (stage I-IV) * Prior/current treatment with anthracycline based chemotherapy followed by anti-HER2 directed therapy or anti-HER2 directed therapy alone * Assessment of LVEF at baseline prior to initiation of anthracycline or anti-HER2 therapy and during anti-HER2 therapy via echocardiogram, cardiac MRI, or MUGA * Prior confirmed diagnosis of cardiotoxicity associated with anti-HER2 based therapy, defined as a decrease in LVEF \> 10% from baseline to \< 53% with symptoms of heart failure (NYHA class II-IV). Subjects in the no cardiotoxicity group (NO-TOX) must meet the following criteria: * History of HER2 positive breast cancer (stage I-IV) * Completion of planned anthracycline and anti-HER2 therapy, or anti-HER2 therapy alone * No symptoms of heart failure (NYHA class II-IV) during and at the end of anthracycline and anti-HER2 therapy * Assessment of LVEF at baseline prior to innitiation of anthracycline or anti-HER2 therapy and during anti-HER2 therapy via echocardiogram, cardiac MRI, or MUGA * Normal LVEF \>53% at each assessment during and at the end of trastuzumab therapy. * Maximum absolute decrease in LVEF \<5% from baseline during and at the end of trastuzumab therapy. * LVEF assessment performed at baseline and at least two time points during trastuzumab therapy. Exclusion Criteria: * Unwilling or unable to give skin biopsies * Contraindications to punch biopsy including but not limited to bleeding diathesis, as determined by the investigator. * Known pre-existing CV disease prior to initiation of breast cancer therapy as determined by the investigator, including * Obstructive coronary artery disease (stenosis \>70%) * Arrhythmia - paroxysmal or persistent atrial arrhythmias, sustained ventricular tachycardia (\>30 seconds), ventricular fibrillation, or cardiac arrest * Cardiomyopathy (EF \<53%) * Heart failure (NYHA class II-IV) * Valvular heart disease with equal to or greater than moderate stenosis or regurgitation