This study assesses changes to the immune cells following hypofractionated radiation-induced DNA damage in breast cancer patients. Radiation therapy may cause immune cells to enter tumors and target cancer cells. The goal of this study is to measure the change in the level of immune cells in the tumor before and after radiation therapy.

PRIMARY OBJECTIVE:

I. To estimate the percent change in immune infiltration at day 3 and day 7 of radiotherapy (RT) relative to baseline (before radiotherapy).

SECONDARY OBJECTIVE:

I. To estimate the degree of deoxyribonucleic acid (DNA) damage at approximately 3 and 7 days after radiotherapy compared to baseline.

II. To examine cancer cell intrinsic immune signaling following radiotherapy.

EXPLORATORY OBJECTIVE:

I. To examine the association between DNA damage and micronuclei formation. II. To examine the association between DNA damage and immune infiltration. III. To examine the association between micronuclei formation and immune infiltration.

OUTLINE:

Patients undergo RT on day 1. Patients also undergo tumor punch biopsies and blood sample collection prior to the first fraction and on days 1, 3, and 7.

Inclusion Criteria:

• Patients >= 18 years of age with biopsy proven invasive breast cancer
• Breast cancer that appears to be superficially accessible to a tumor punch biopsy
• Patients thought to derive clinical benefit from palliative RT to the breast/chestwall
• In discussions with the medical oncologist, if clinically reasonable, systemic therapy will be held during RT

Exclusion Criteria:

• A history of prior radiation to the area requiring radiation for which the attending physician believes reirradiation could not be safely delivered
• Pregnancy
• Active usage of anticoagulant medications that are considered to pose an increased risk of tumor punch biopsies
• Receipt of immunotherapy or chemotherapy 7 days prior to start of RT

Patients with breast cancer that appears to be superficially accessible to a tumor punch biopsy