The purpose of this study is to test the ability of a breast MRI biopsy to accurately diagnose a complete tumor response to the neoadjuvant chemotherapy (NAC) that the patient just finished. Numerous studies have shown that MRI has the highest accuracy for diagnosing a complete tumor response. The investigator wants to see if in a certain group of women who's breast cancer is no longer visible on the post-treatment MRI that the biopsy specimens from a MRI guided biopsy will accurately diagnose a complete tumor response to treatment which may in the future make breast surgery unnecessary in some women.
Inclusion Criteria: * Women age 18 years or older * Confirmed histologic diagnosis of operable HER2 overexpressing (ER\<10%, PR\<10%, and HER2 2+ or FISH amplified) OR triple negative (ER\<10%, PR\<10%, and HER2 0/1+ or 2+/FISH not amplified) OR ER positive invasive ductal or invasive lobular breast cancer including MSKCC pathology confirmation * Operable breast cancer treated with NAC undergoing either breast conservation or total Mastectomy who have had a post-NAC clinical bilateral breast MRI demonstrating a complete imaging response, which is defined as no residual tumor enhancement. * No indication of distant metastases (M0) * Tumor site amenable to MRI guided biopsy as determined by the radiologist * Definitive surgery being performed at MSKCC within within 0-60 days of completing NAC * ECOG performance status score of 0 to ≤ 2 and or KPS performance status score of 80% to 100% * Women of childbearing potential (WOCBP) must not be pregnant. * Women must not be breastfeeding * Willing and able to provide informed consent and adhere to the study visit schedule and plan as specified in this protocol Exclusion Criteria: * Medical history and concurrent disease: * Prior history of treated breast cancer * Any underlying medical or psychiatric conditions, which in the opinion of the investigator, will make performing the study intervention hazardous or obscure the interpretation of the results * Prohibited Treatments and/or Therapies: * Prior history of breast cancer surgery and/or radiotherapy.