5 vs. 9-day Course of Whole Breast Radiotherapy With Boost for Early-stage Breast Cancer

Eligibility Criteria

• * Female participant aged ≥ 18 years.
• * Participants \> 50 years must have at least one of the following risk factors:
• * Grade 3 invasive histology
• * Estrogen receptor positivity less than 5%
• * Lymphovascular invasion
• * Margins \<2mm on surgical pathology
• * Extensive intraductal component
• * Participants ≤ age 50 need no additional risk factors.
• * Histologically confirmed invasive carcinoma or Ductal Carcinoma In Situ (DCIS) of the breast.
• * Breast cancer stage (AJCC v8) T0-3, N0, M0. T0 N0 is allowed if whole breast radiation is recommended by the treating physician.
• * Lumpectomy within 84 days of the start of radiation.
• * ECOG Performance Status ≤ 2, or KPS ≥ 50
• * Negative inked histologic margins from lumpectomy, with the exception of a focus of positive margin at the pectoralis fascia.
• * Negative pregnancy test for participants of childbearing potential, evidence of permanent surgical sterilization, or post-menopausal status. The post-menopausal status will be defined as having been amenorrheic for 12 months without an alternative medical cause. The following age-specific requirements apply:
• * \< 50 years of age:
• * Amenorrheic for ≥ 12 months following cessation of exogenous hormonal treatments; and
• * Luteinizing hormone and follicle-stimulating hormone levels in the post-menopausal range for the institution
• * ≥ 50 years of age:
• * Amenorrheic for 12 months or more following cessation of all exogenous hormonal treatments; or
• * Had radiation-induced menopause with last menses \>1 year ago; or
• * Had chemotherapy-induced menopause with last menses \>1 year ago
• * Sexually active participants of childbearing potential must agree to use highly effective method of contraception (defined in Section 5.4.1) during the course of radiation and for 30 days after radiation.
• * Able to provide informed consent and willing to sign an approved consent form that conforms to federal and institutional guidelines.
• * Bilateral breast cancer.
• * Prior radiation therapy to the chest.
• * Prior chemotherapy.
• * Recurrent disease.
• * Known metastases or node positive.
• * Major chest surgery which is expected to impact study participation 8 weeks prior to starting study drug.
• * Prior breast malignancy in either breast.
• * The diagnosis of any other malignancy which, in the opinion of the Investigator, is likely to negatively impact the subject's safety or ability to participate in the study.
• * Current evidence of uncontrolled, significant intercurrent illness including, but not limited to, the following conditions:
• * Cardiovascular disorders:
• * Congestive heart failure New York Heart Association Class III or IV, unstable angina pectoris, serious cardiac arrhythmias.
• * Stroke (including transient ischemic attack \[TIA\]), myocardial infarction (MI), or other ischemic events, or thromboembolic event (e.g., deep venous thrombosis, pulmonary embolism) within 3 months before the first dose.
• * Any other condition that would, in the Investigator's judgment, contraindicate the participant's participation in the clinical study due to safety concerns or compliance with clinical study procedures (e.g., infection/inflammation, intestinal obstruction, unable to swallow, social/ psychological issues, etc.)
• * Significant post lumpectomy complications requiring an unplanned re-operation for surgical complications or admission for IV antibiotics. Re-operation for margins evaluation or nodal evaluation is acceptable. Draining of a seroma is not considered a complication unless it has become infected.
• * Breast neuroendocrine carcinoma or sarcoma histology.
• * Radiation sensitizing disease or condition (e.g. connective tissue disease, li fremani, etc.).
• * Medical, psychiatric, cognitive, or other conditions that may compromise the participant's ability to understand the participant information, give informed consent, comply with the study protocol or complete the study.
• * Participants receiving concurrent radiation sensitizing medications or therapies.