Summary

This randomized phase III trial studies if not giving regional radiotherapy is just as good as using regional radiotherapy in keeping breast cancer from coming back in patients with estrogen receptor (ER) positive, HER2 negative node positive low risk breast cancer who have undergone breast conserving surgery or mastectomy. Women with ER positive breast cancer normally will receive endocrine therapy and some may receive chemotherapy to help prevent the cancer from coming back. Many women will also receive radiotherapy to the whole breast/chest area and the surrounding lymph glands (called regional radiotherapy). Radiation therapy uses high energy x-rays to kill tumor cells and shrink tumors. It is not known whether patients with low risk breast cancer need to receive regional radiotherapy. As a result, some women may be getting regional radiotherapy who do not need it and be exposed to the side effects of their treatment without benefit. This study will help to determine if regional radiotherapy can be omitted for low risk ER positive node positive breast cancer patients.

Objectives

PRIMARY OBJECTIVE:
I. To compare the breast cancer recurrence-free interval (BCRFI) between patients that received regional radiation therapy (RT) or not, defined as time from randomization to time of invasive recurrent disease in the ipsilateral chestwall, breast, regional nodes, distant sites or death due to breast cancer (BC).

SECONDARY OBJECTIVES:
I. To compare the invasive disease-free survival (DFS) between patients that received regional RT or not.
II. To compare the breast cancer mortality between patients that received regional RT or not.
III. To compare the overall survival (OS) between patients that received regional RT or not.
IV. To compare the locoregional recurrence-free interval (LRRFI) between patients that received regional RT or not.
V. To compare the distant recurrence-free interval (DRFI) between patients that received regional RT or not.
VI. To compare the toxicity between patients that received regional RT or not.
VII. To compare arm volume and mobility measurements between patients that received regional RT or not.
VIII. To compare patient reported outcomes (PROs) and the quality of life (QOL) between patients that received regional RT or not. (Enrollment completed August 2,2022)
IX. To compare the cost effectiveness between patients that received regional RT or not. (Enrollment completed August 2,2022)

TERTIARY OBJECTIVES:
I. To establish a comprehensive tumor bank linked to a clinical database for the further study of predictive and prognostic biomarkers in breast cancer.
II. To evaluate the ability of intrinsic subtype measured by immunohistochemistry (IHC) to predict BCRFI, LRRFI, DRFI and the effect of regional RT on these outcomes.
III. To evaluate other radiation sensitivity signatures to prognosticate and predict effect of regional RT.
IV. To describe the prevalence of detectable baseline circulating tumor deoxyribonucleic acid (DNA) (ctDNA) in node positive low risk estrogen receptor (ER) positive breast cancer and evaluate its prognostic ability.

OUTLINE: Patients are randomized to 1 of 2 arms.

ARM 1: Following breast conserving surgery (BCS), patients receive whole breast irradiation (WBI) daily Monday to Friday for 16-21 or 25-32 fractions. Patients who underwent mastectomy do not receive RT.

ARM 2: Following BCS, patients receive WBI plus RT to the regional nodes (supraclavicular, non-dissected axillary, and internal mammary) daily Monday to Friday for 16-21 or 25-32 fractions. Patients who have had a mastectomy receive RT to the chest wall and regional nodes (supraclavicular, non-dissected axillary, and internal mammary).

Patients undergo blood sample collection throughout the study.