Pembrolizumab in Treating Patients With Stage IV Metastatic or Recurrent Inflammatory Breast Cancer or Triple-Negative Breast Cancer Who Have Achieved Clinical Response or Stable Disease to Prior Chemotherapy

Inclusion Criteria: * Is willing and able to provide written informed consent for the trial * Is a female or male and \>/= 18 years of age * Has histological confirmation of HER2 normal breast carcinoma with a clinical diagnosis of IBC based on presence of inflammatory changes in the involved breast, including diffuse erythema and edema (peau d'orange), with or without an underlying palpable mass involving the majority of the skin of the breast; pathological evidence of dermal lymphatic invasion should be noted but is not required for diagnosis of inflammatory breast cancer regardless estrogen receptor (ER)/progesterone receptor (PR) status; OR has histological confirmation of triple negative breast carcinoma (HER2 normal, ER/PR \< 10%) without clinical diagnosis of IBC * Has stage IV or recurrent disease that has been treated * Has clinical response or stable disease for minimum of two months (three cycles of every three week chemotherapy or 8 weeks of weekly regimen, etc.) after receiving any prior chemotherapy for metastatic/recurrent disease; a minimum of two cycles (6-8 weeks) of chemotherapy is required to determine clinical response. Per RECIST criteria 1.1, Clinical response for measurable disease is defined as complete response (CR) or partial response (PR); for non-measurable disease only (i.e. bone metastasis, ascites, pleural effusion, and pathological lymph nodes \>/= 10 to \<15 mm short axis) is defined as persistence of one or more non-target lesion(s) and no…