Propranolol and Pembrolizumab for Tumor Re-sensitization and Treatment of Patients With Checkpoint Inhibitor Refractory Metastatic or Unresectable Triple Negative Breast Cancer

Inclusion Criteria: * Age \>= 18 years of age * Have pathologically confirmed diagnosis of unresectable or metastatic triple negative breast cancer (TNBC) with no curative treatment options * No chemotherapy, radiotherapy, or major surgery within 4 weeks of protocol treatment * Checkpoint inhibitor refractory patients (i.e., no longer responding to chemotherapy and checkpoint inhibitor) who have disease progression on prior line of chemotherapy and pembrolizumab, and, who in the opinion of the physician, can continue checkpoint inhibitor * Patients must be agreeable to pre- and 6-week post treatment biopsy in part 1 of the study * The pre-treatment biopsy for this study must be taken at least 4 weeks after all previous chemotherapy (pembrolizumab is allowed during this period) * Participants of child-bearing potential must agree to use adequate contraceptive methods (e.g. hormonal or barrier method of birth control; abstinence) prior to study entry. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately * Have an Eastern Cooperative Oncology Group (ECOG) Performance Status of =\< 1 * Platelets \>= 100,000/uL * Hemoglobin \>= 9.0 g/dL * Absolute neutrophil count (ANC) \>= 1500/uL * Total bilirubin =\< institutional upper limit of normal (ULN) * Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase \[SGOT\]) and alanine aminotransferase (ALT) …