The purpose of this study is to test whether patients with breast cancer who are being treated with non-anthracycline trastuzumab therapy can safely be monitored for heart related side effects less often than usual.

Inclusion Criteria:

• Age >/= 18 years
• Newly diagnosed histologically confirmed primary invasive breast carcinoma (Stage I-IV)
• Pathologically confirmed HER2-positive breast cancer
• Planned to receive trastuzumab-based therapy for a minimum of 12 months, or started trastuzumab-based therapy within the last weeks with a planned duration of at least 12 months.
• Normal LV systolic function (EF greater than or equal to the institutional lower limit of normal)
• William and able to comply with the requirements of the protocol

Exclusion Criteria:

• Planned to receive an anthracycline-based regimen
• Prior history of treatment with anthracycline chemotherapy
• History of cardiovascular including cardiomyopathy, heart failure, or any other clinically significant cardiovascular disease (as determined by the investigator)
• Uncontrolled hypertension, defined as systolic blood pressure >/= 160 mmHg and/or diastolic blood pressure >/= 90 mmHg (as determined by the investigator)

A member of the patient's treatment team, the protocol investigator, or research team at MSK will identify potential research participants. The preliminary screen of eligibility will be confirmation of the diagnosis of HER2-positive breast cancer. A member of the treatment team will discuss the study and the possibility of enrollment in the study with potential subjects that meet this eligibility criterion. The study will be conducted at the Evelyn H. Lauder Breast Center of MSK as well as at the regional MSK network sites. Recruitment at both main and regional network sites will ensure the enrollment of diverse populations of different ages, races, and ethnic groups onto the study. Patients will then be consented to the study.

In most cases, the initial contact with the prospective subject will be conducted either by the treatment team, investigator or the research staff working in consultation with the treatment team.

• Memorial Sloan Kettering Cancer Center supports the international committee of medical journal editors (ICMJE) and the ethical obligation of responsible sharing of data from clinical trials. The protocol summary, a statistical summary, and informed consent form will be made available on clinicaltrials.gov when required as a condition of Federal awards, other agreements supporting the research and/or as otherwise required. Requests for deidentified individual participant data can be made beginning 12 months after publication and for up to 36 months post publication. Deidentified individual participant data reported in the manuscript will be shared under the terms of a Data Use Agreement and may only be used for approved proposals. Requests may be made to: crdatashare@mskcc.org.