This phase III trial compares the effect of low dose tamoxifen to usual hormonal therapy, including aromatase inhibitors, in treating post-menopausal women with hormone positive, HER2 negative early stage breast cancer. Tamoxifen is in a class of medications known as antiestrogens. It blocks the activity of estrogen (a female hormone) in the breast. This may stop the growth of some breast tumors that need estrogen to grow. Aromatase inhibitors, such as anastrozole, letrozole, and exemestane, prevent the formation of estradiol, a female hormone, by interfering with an aromatase enzyme. Aromatase inhibitors are used as a type of hormone therapy to treat postmenopausal women with hormone-dependent breast cancer. Giving low dose tamoxifen may be more effective compared to usual hormone therapy in treating post-menopausal women with hormone-positive, HER2 negative early stage breast cancer.

Who can Participate

Inclusion Criteria: Unilateral invasive adenocarcinoma of the breast that is histologically confirmed Invasive breast cancer is estrogen receptor positive in ≥ 10% of cells HER2 negative by current American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines The patient must have a multigene assay with a low-risk score, including any of the following (if more than one genomic assay was obtained, both are required to be low-risk): Oncotype DX recurrence score ≤ 25 Mamma Print low risk Prosigna risk of recurrence ≤ 40 Tumor size must be ≤ 3 cm by pathologic evaluation Adequate surgical removal of all clinically evident disease in the breast with either breast conserving surgery or mastectomy. Negative margins on final pathology are required. Additional excisions may be performed to obtain clear margins before registration No clinical (cN1, cN2, cN3) or pathologic (pN1mi, pN1, pN2, or pN3) evidence of lymph node involvement on either needle biopsy or surgical lymph node assessment. Patients with pN0(i+) or pN0 (mol+) are eligible Surgical axillary staging (sentinel lymph node biopsy ± axillary lymph node dissection) is completed according to physician discretion For patients with negative preoperative axillary ultrasonography, clinicians may selectively choose to forego surgical axillary staging. Ipsilateral axillary ultrasound showing no lymph node involvement with no evidence of lymphadenopathy or suspicious thickening is required in this scenario No pathological tumor size > 3 cm or pT4 No definitive clinical or radiologic evidence of metastatic disease Detailed eligibility criteria is available on ClinicalTrials.gov. These requirements will be discussed with your doctor and/or study representative. ClinicalTrials.gov to learn more about this study.

Study ID

More information available at ClinicalTrials.gov: NCT06671912