Neoadjuvant Endocrine Therapy, Palbociclib, Avelumab in Estrogen Receptor Positive Breast Cancer

Inclusion Criteria: * Stage II-III ER-positive breast cancer * Tumor evaluable either by ultrasound or by touch. * Age ≥ 18 years. * Eastern Cooperative Oncology Group performance status of 1 or less. * Adequate organ and bone marrow function within 28 days prior to registration. * Females of child-bearing potential and males must agree to use adequate contraception prior to study entry, for the duration of study participation, and for 30 days following completion of therapy. * Females of child-bearing potential must have a negative pregnancy test within 7 days prior to registration on study. * Patients must have the ability to understand and the willingness to sign a written informed consent prior to registration on study Exclusion Criteria: * Evidence of metastatic disease or inflammatory breast cancer. * Patients not felt to be sensitive to endocrine therapy, such that a neoadjuvant endocrine-based approach would not be appropriate (i.e. PR-negative, high grade/Ki67, high gene expression profile, clinically aggressive presentation) * Previous treatment with endocrine therapy within the last 10 years (i.e. tamoxifen, aromatase inhibitors). * Previous treatment with CDK4/6 inhibitors, or immune checkpoint inhibitors. * Use of SSRIs and/or any concomitant use of medications outlined in section 6.5 within 4 days prior to enrollment. If patients are on stable doses and there are no good alternatives, the treating physician may discuss with Study Chair. * May not be receiving…