A Study of Cyclophosphamide, Methotrexate, Fluorouracil (CMF) for People With Breast Cancer

Inclusion Criteria:

* Patients must have histologically confirmed adenocarcinoma of the breast confirmed at MSK. The patient must have had diagnostic biopsy or completion of primary surgical management, within 3 months of enrollment. Results of HER-2/neu, estrogen receptor, and progesterone receptor are required for study entry.
* Patients must be ≥ 70 years of age.
* Patients must have ECOG performance status \>2 (Karnofsky score of ≥ 60%).
* Patients may have received hormonal therapy for the purpose of chemoprevention.
* Adjuvant/neoadjuvant chemotherapy decision to treat based on the discretion of investigator
* Cohort 1 only: Patients have any histology except Her 2 Neu positive in the adjuvant or neoadjuvant setting
* Cohort 2 only: Patients have triple negative (ER- (10%) PR-Her 2 Neu -) in the neoadjuvant setting
* Cohort 2 only: Patients have received at least 1 dose of carboplatin/paclitaxel +/- pembrolizumab in the neoadjuvant setting

Required Organ Function

Adequate hematologic function defined as follows:

* Absolute neutrophil count (ANC) ≥ 1,500 cells/mm3
* Platelets ≥ 100,000 cells/mm3

Adequate renal function defined as follows:

° Creatinine clearance (CrCL) of \>30 mL/min by the Cockcroft-Gault formula:

CrCl (mL/min) = \[(\[140 - age(years)\] x weight (kg))/72 x creatinine (mg/dL)\] (x 0.85 for female patients)

Adequate hepatic function defined as follows:

* Total bilirubin ≤ 1.5 x institutional upper limit of normal (ULN) (patients with known Gilbert's disease who have bilirubin level ≤ 3 x institutional ULN may be enrolled)
* AST and ALT ≤3 x institutional ULN

  * Patients or their Legally Authorized Representative must give written, informed consent indicating their understanding and willingness to participate in the study.

Exclusion Criteria:

* Stage IV breast cancer
* CARG score- high Frail 4 or more as assessed by CAIT
* Her 2 Neu positive 3+/amplified breast cancer
* No prior chemotherapy within 1 year of study enrollment
* Cohort 2 only: patients may not receive pembrolizumab during dd CMF treatment