A patient needs ALL of the following conditions met

Female patients must be greater or equal to 18 years of age

Must be premenopausal(PM) at the time of pre-entry defined as

Age 50 or under with spontaneous menses within 12 months; or

Age greater than 50-60 with spontaneous menses within 12 months plus FSH and estradiol levels in the PM range; or

Amenorrhea due to IUD or prior uterine ablation must have FSH and estradiol levels in the PM range; or

Prior hysterectomy must have FSH and estradiol levels in the PM range

ECOG performance status of less than or equal to 2 or Karnofsky greater than or equal to 60%

Ipsi- or contralateral synchronous breast cancer if the highest stage tumor meets entry criteria

Patients who undergo a lumpectomy, the margins of the resected specimen or re-excision must be histologically free of invasive tumor and DCIS with no ink on tumor

For patients who undergo mastectomy, margins free of residual gross tumor

Patient must have undergone axillary staging with SNB TAD, or ALND

Various staging criteria must be met postoperatively according to AJCC 8th edition criteria

Oncotype DX RS (recurrence score) requirements: reach out to study team

Patients with a "Low Risk" or "MP1" MammaPrint result must have eligibility assessed with an Oncotype DX RS at pre-entry. If MP2, these patients are not eligible

Must be ER and/or PgR-positive by current ASCO/CAP guidelines based on local testing results. Patients with greater than or equal to 1% ER and/or PgR staining by IHC will be classified as positive

Must be HER2-negative by current ASCO/CAP guidelines based on local testing results

Time between the last surgery for breast cancer and pre-entry must be no more than 16 weeks

Short course of endocrine therapy of less than 6 weeks duration before pre-entry is acceptable

HIV-infected patients on effective anti-retroviral therapy with undetectable viral load within 6 months are eligible for this trial

Radiation therapy should be used according to standard guidelines; the intended radiation therapy should be declared prior to pre-entry

(Not a complete list)

Definitive clinical or radiologic evidence of metastatic disease

pT4 tumors, including inflammatory breast cancer

History of ipsilateral or contralateral invasive breast cancer

If prior ipsilateral DCIS was treated with lumpectomy and XRT (ionizing radiation therapy), a mastectomy must have been performed for the current cancer

Life expectancy of less than 10 years due to co-morbid conditions

Most recent labs showing

ANC less than 1200/mm3;

Platelet count less than 100k/mm3

Hemoglobin less than 10 g/dL;

Total bilirubin greater than ULN for the lab or greater than 1.5 x ULN for patients who have a bilirubin elevation due to Gilbert's disease or similar syndrome

AST(SGOT)/ALT(SGPT): greater than 3 × institutional ULN

Renal function of GFR less than 30 mL/min/1.73m2

Patients with known history or current symptoms of cardiac disease, or history of treatment with cardiotoxic agents, should have a clinical risk assessment of cardiac function. To be eligible for this trial, patients should be class 2B or better

Non-epithelial breast malignancies such as sarcoma or lymphoma

Any treatment with radiation therapy, chemotherapy, or biotherapy administered for the currently diagnosed breast cancer prior to pre-entry. Prior tamoxifen given for breast cancer prevention is allowed. Prior AI or GnRH for fertility preservation is allowed

Hormonally based contraceptive measures must be discontinued prior to pre-entry

Patients with evidence of chronic HBV infection are ineligible unless the HBV viral load is undetectable on suppressive therapy. Patients with a history of HCV infection are ineligible unless they have been treated and cured or have an undetectable HCV viral load if still on active therapy

Pregnancy or lactation at the time of pre-entry

(Not a complete list)