RADIANT: Pre-op Radiation With Abemaciclib and Letrozole

Inclusion criteria

• Histologically and/or cytologically confirmed diagnosis of invasive (ductal, lobular or mixed histology), Clinically inapparent tumor that is not palpable. (cT1-T2N0)disease. Minimum tumor size of 1.5 cm
• Expression of ER or progesterone receptors (PR)and negative expression of HER2 per American Society of Clinical Oncology, (ASCO) Common Alerting Protocol (CAP) guidelines
• Oncotype diagnosis (DX) Breast Recurrence score of less than 25 on core biopsy specimen
• Post-menopausal status defined:
• age \<60 with amenorrhea for at least 12 months in the absence of prior chemotherapy, tamoxifen, toremifene, or ovarian suppression and estradiol and FSH (follicle stimulating hormone) in postmenopausal range.
• No clinical suspicion of metastasis disease
• Eastern Cooperative Oncology Group (ECOG) performance status of follicle stimulating hormone (PFS) ≤2
• Eligible to undergo surgery, either lumpectomy or mastectomy for local treatment of the breast cancer
• Able to swallow oral medications
• Adequate organ function for all of the following:
• Absolute Neutrophil (ANC) \>1.5 x 10/L Platelets \>100 x 10/L Hemoglobin \>8 g/dL - May receive erythrocyte transfusions to achieve this level Total Bilirubin \<1.5 x Upper Limit of Normal (ULN) Alanine Aminotransferase (ATL) and Aspartate Aminotransferase (AST) \<3 x ULN
• HR positive/HER2 -negative breast cancers are allowed as long as no other exclusions exist

Exclusion criteria

• History of ipsilateral breast cancer
• Prior treatment with CDK4/6 inhibitors or aromatase inhibitors
• History of chest wall or ipsilateral breast radiation
• Inflammatory breast cancer
• Needs neoadjuvant chemotherapy
• Presence of distant metastatic disease
• Contraindication for surgery
• Uncontrolled hypertension (systolic blood pressure \>190 mm Hg or diastolic blood pressure \>100 mm Hg)
• Any condition including the presence of laboratory abnormalities, which, in the opinion of the investigator places the subject at unacceptable risk if he/she were to participate in the study
• Life expectancy \< 12 weeks
• History of allergy or hypersensitivity to any of the study drugs
• Any significant medical condition, laboratory abnormality, or psychiatric illness
• Serious and/or uncontrolled preexisting medical condition
• Has had major surgery within 14 days prior to enrollment
• Has received an experimental treatment in a clinical trial within the last 30 days or 5 half-lives, whichever is longer, prior to enrollment, or is currently enrolled in any other type of medical research
• Has active systemic bacterial infection
• Personal history of any of the following conditions: syncope of cardiovascular etiology, ventricular arrhythmia of pathological origin (including, but not limited to, ventricular tachycardia and ventricular fibrillation), or sudden cardiac arrest