Study of Erlotinib and Metformin in Triple Negative Breast Cancer

Inclusion Criteria: * Confirmed pathologic diagnosis of triple negative breast cancer, OR Prior diagnosis of ER or P-R positive breast cancer \[HER2 negative\] that is demonstrated to be both ER and P-R negative (no or rare staining) on the patient's most recent biopsy. * Patients with measurable or non-measurable metastatic disease (RECIST 1.1). * At least one prior treatment for metastatic disease. * Availability of adequate tumor tissue for exploratory analysis and plan to obtain the material. * Patients must have recovered from the acute toxic effects of all prior chemotherapy, immunotherapy, or radiotherapy prior to entering this study. No chemotherapy or radiotherapy may be given within 2 weeks prior to the start of protocol treatment. * Patients must be ≥ 18 and \< 80 years old. * Performance Status: Eastern Cooperative Oncology Group (ECOG) 0-2. * Life expectancy of greater than 12 weeks. * Patients must have recovered from uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris or cardiac arrhythmia. * Required Laboratory Values: Absolute neutrophil count (ANC) ≥1,250/mm3, platelets ≥75,000/mm3, hemoglobin ≥8.5 g/dL, total bilirubin ≤1.5 x ULN, Aspartate Aminotransferase (AST)/Alanine Aminotransferase (ALT) ≤3.0 x ULN, alkaline phosphatase ≤2.5 x ULN, Patients must have either a normal serum creatinine (\<= IULN) OR estimated creatinine clearance ≥ 60 ml/min (Cockcro…