COX Inhibition and Biomarkers During Neoadjuvant Chemoendocrine Therapy for ER+, HER2- Stage I-III Breast Cancer

Inclusion Criteria: 1. Provision of signed and dated informed consent form 2. Stated willingness to comply with all study procedures and availability for the duration of the study 3. Male or female, aged 18 or older 4. Newly diagnosed with ER+/HER2- stage I-III breast cancer according to American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines and the 8th edition of the American Joint Committee on Cancer (AJCC); ER positive is defined as ≥ 1% positive nuclear staining 5. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0-2 6. Life expectancy ≥ 6 months 7. Women of childbearing potential and men must agree to use adequate contraception (see section 5.4) prior to study entry and for at least 3 months following the last dose of tamoxifen 8. If genomic profiling has been performed (OncotypeDx, Mammaprint or other), then the score must be in a medium- or high-risk range. 9. Adequate Organ Function as described below. There are no requirements regarding recent transfusions Absolute Neutrophil Count ≥1000/mm3 Platelets ≥100,000/mm3 Hemoglobin ≥9 g/dL Serum Creatinine or Glomerular Filtration Rate (GFR) ≤ 1.5 x upper limit of normal (ULN) Bilirubin ≤ 1.5 x ULN (except in patients with Gilbert's disease, where bilirubin to 4x ULN or direct bilirubin ≤ ULN is allowed) Aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) ≤ 2.5 x ULN Alkaline phosphatase ≤ 2.5 x ULN 10. Ability to take oral medication Exclusion Criteria: 1. Receipt of any systemic treatment for the current diagnosis of breast cancer (breast biopsy, excisional biopsy, or other local therapy is acceptable as long as residual disease is present and is appropriate for systemic chemotherapy and additional curative intent resection) 2. Current use of anticoagulant (e.g. warfarin (Coumadin), heparin, direct oral anticoagulants (DOAC)) within 72 hours of registration 3. Pregnancy or lactation 4. Currently in prison 5. Requirement for supplemental oxygen therapy 6. Current active cancer other than breast cancer 7. History of severe bleeding that, in the treating investigator's opinion, would put the patient at increased risk with daily 325 mg aspirin use 8. Known allergic reactions to aspirin, tamoxifen, doxorubicin, cyclophosphamide, or paclitaxel 9. Participants classified according to the New York Heart Association classification as having Class II - IV heart disease (section 12.2) 10. History of thrombosis or cerebrovascular accident