This study is being done to see if losartan affects the chances of developing radiation-induced heart failure in patients who are receiving radiation therapy as part of standard of care treatment for breast cancer.

The interventions involved in this study are:

• Losartan
• Radiation Therapy (standard of care)

This is a pilot study examining whether losartan prevents radiation therapy-induced myocardial fibrosis (thickening of the heart tissue), which can cause heart failure, in breast cancer patients receiving radiation therapy.

Losartan is an U.S. Food and Drug Administration (FDA) approved drug used to treat hypertension (high blood pressure) and heart failure. The U.S. Food and Drug Administration (FDA) has not approved losartan for use in the treatment of breast cancer.

The FDA has approved radiation therapy as a treatment option for breast cancer.

The research study procedures include: screening for eligibility and study treatment including evaluations and follow up visits. It is expected participants will be on the study for 1 year.

It is expected that about 10 people will take part in this research study.

Inclusion Criteria:

->18 years of age

• Non-metastatic Breast Cancer patients who are scheduled to receive conventional left breast/chest wall RT inclusive of treatment to the internal mammary lymph nodes (IMNs)
• Prior chemotherapy is permitted
• Patients must have Left-sided Breast Cancer
• Ability to understand and the willingness to sign a written informed consent document
• No contraindication to MRI

Exclusion Criteria:

• Person who is pregnant or breastfeeding.
• Patient unable to swallow oral medication.
• Patients receiving any other investigational agent will not be excluded from study eligibility, unless the patient is already enrolled in an interventional study evaluating cardiac toxicity
• Patients already receiving ACE/ARBs.
• Patients with a history of allergic reactions to Losartan biosimilars.

The Dana-Farber / Harvard Cancer Center encourages and supports the responsible and ethical sharing of data from clinical trials. De-identified participant data from the final research dataset used in the published manuscript may only be shared under the terms of a Data Use Agreement. Requests may be directed to: [contact information for Sponsor Investigator or designee]. The protocol and statistical analysis plan will be made available on Clinicaltrials.gov only as required by federal regulation or as a condition of awards and agreements supporting the research.

Data can be shared no earlier than 1 year following the date of publication

Contact the Partners Innovations team at http://www.partners.org/innovation