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

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 increase in overall tumor burden.

Is HER2 normal, defined as HER2 0 or 1+ by IHC and negative by FISH if performed; or HER2 is 2+ by IHC and negative by FISH; or HER2 negative by FISH if IHC is not performed.

Has a performance status of 0-1 on the Eastern Cooperative Oncology Group (ECOG) performance scale

Has adequate organ function as determined by the following laboratory values:

ANC \>/= 1000 /mcL, Platelets \>/=100,000 /mcL, Hgb \>/= 9 g/dL, creatinine levels \< 1.5 x ULN, Total bilirubin \</= 1.5 x ULN, ALT and AST \</= 2.5 x ULN or \</=5 x ULN for participants with liver metastases.

Participants of childbearing potential should be willing to use effective methods of birth control or be surgically sterile, or abstain from heterosexual activity for the course of the study through at least 4 months after the last dose of study drug. Participants of childbearing potential are those who have not been surgically sterilized or have not been free from menses for \> 1 year. Effective methods of birth control include 1). Use of hormonal birth control methods: pills, shots/injections, implants (placed under the skin by a health care provider), or patches (placed on the skin); 2).Intrauterine devices (IUDs); 3).Using 2 barrier methods (each partner must use 1 barrier method) with a spermicide. Males must use the male condom (latex or other synthetic material) with spermicide. Females must choose either a Diaphragm with spermicide, or Cervical cap with spermicide, or a sponge (spermicide is already in the contraceptive sponge).

Has negative serum or urine pregnancy test for participants of childbearing potential

What this study is about