Study Of Single-dose Cyclophosphamide +Pembrolizumab In Patients With Metastatic Triple Negative Breast Cancer

Inclusion Criteria

• Written informed consent and HIPAA authorization for release of personal health information. NOTE: HIPAA authorization may be included in the informed consent or obtained separately.
• Age ≥ 18 years at the time of consent.
• Have measurable disease based on RECIST 1.1 (see section 6.7 for details).
• ECOG Performance Status ≤ 1 as defined in the protocol ECOG Performance Status.
• Subject must have histologically confirmed stage IV TNBC (ER-, PR-, HER2-negative) and have received at least 1 prior line of systemic therapy.
• ER- and PR-negative: defined as < 1% staining by immunohistochemistry (IHC)
• HER2-negative disease, defined as IHC 0-1+ or fluorescence in situ hybridization (FISH) ratio < 2.0
• Patients with stable brain metastases will be allowed provided the following criteria are met:
• Brain radiation was already provided at least 4 weeks prior to initiating study treatment
• The subject has no new or progressive neurologic symptoms AND neurological symptom stability for the last 4 weeks prior to the study
• The subject has been off of corticosteroids for at least 7 days prior to trial treatment
• The subject does not have carcinomatous meningitis
• Demonstrate adequate organ function as defined in the table below; all screening labs to be obtained within 72 h of initiating study treatment.
• Females of childbearing potential must have a negative serum pregnancy test within 72 hrs prior to treatment. NOTE: Females are considered of child bearing potential unless they are surgically sterile, have a congenital acquired condition that prevents childbearing (have undergone a hysterectomy, bilateral tubal ligation/occlusion, bilateral salpingectomy or bilateral oophorectomy at least 6 weeks prior to screening) or they are naturally postmenopausal for at least 12 consecutive months without an alternative medical cause. In women < 45 years of age a high follicle stimulating hormone level in the postmenopausal range may be used to confirm a post-menopausal state in women not using hormonal contraception or hormonal replacement therapy. In the absence of 12 months of amenorrhea, a single FSH measurement is insufficient.
• Female patients of childbearing potential should be willing to use appropriate birth control as outlined in Section 5.2.8, or abstain from heterosexual activity for the course of the study through 120 days after the last dose of study medication.
• Male subjects of childbearing potential must agree to use an adequate method of contraception as outlined in Section 5.2.8, starting with the first dose of study therapy through 120 days after the last dose of study therapy.
• Consent for the use of any residual material from biopsy (archival tissue) and serial blood draws will be required for enrollment; fresh biopsy (pre and post dose) of tumor tissue will be optional. NOTE: Patients without adequate tissue for bio correlates will not be excluded or required to have a repeat biopsy.
• As determined by the enrolling physician or protocol designee, the subject should be able to understand and comply with study procedures for the entire length of the study.
• Has a LVEF within the normal institutional range (or ≥ 50%) based on ECHO or MUGA.

Exclusion Criteria

• Active infection requiring systemic therapy
• Pregnant or breastfeeding (NOTE: breast milk cannot be stored for future use while the mother is being treated on study).
• Has a known history of active Bacillus Tuberculosis (TB)
• Hypersensitivity to pembrolizumab or any of its excipients.
• Has a known additional malignancy that is active and/or progressive requiring treatment; exceptions include basal cell or squamous cell skin cancer, in situ cervical or bladder cancer, or other cancer for which the subject has been disease-free for at least five years.
• Has had prior chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to receipt of study medication or who has not reco