title: Targeting the host immune system: PD-1 and PD-L1 antibodies and breast cancer.
abstract: This article describes the role of the PD-1 axis and reviews current data and future directions inhibiting PD-1 and PD-L1 in breast cancer.
  
  
  
  Four phase I monotherapy expansion trials in patients with metastatic breast cancer have demonstrated low but durable single agent responses to PD-1 and PD-L1 inhibitors, ranging from 4.8 to 19%. Higher response rates are seen in triple negative breast cancer, compared with hormone receptor positive disease. Variability in requirements for tumor PD-L1 expression, and variations in testing complicate cross trial comparisons. A fifth phase Ib trial reported a 38% response rate in metastatic triple negative breast cancer treated with the combination of a PD-L1 inhibitor and nab-paclitaxel chemotherapy. Treatment is generally well tolerated, with low rates of immune toxicity including hypothyroidism, pneumonitis, hepatitis, colitis, and hypophysitis, occurring even months after the end of therapy.
  
  
  
  Immune checkpoint inhibitor therapy has recently been shown to have clinical efficacy in the treatment of breast cancer. The most compelling data are in the triple negative subtype, with responses documented in hormone receptor positive disease as well. Numerous trials are evaluating various combination strategies and biomarkers in early and late stage disease to enhance immunogenicity and response.
authors.affiliation: aDepartment of Medical Oncology, Dubai Hospital, UAE bUniversity of California San Francisco Helen Diller Family Comprehensive Cancer Center, San Francisco, CA.
authors.forename: Shaheenah
authors.initials: S
authors.lastname: Dawood
authors.forename: Hope S
authors.initials: HS
authors.lastname: Rugo
mesh_terms: D000418:Albumins / Q000627:therapeutic use; D000971:Antineoplastic Combined Chemotherapy Protocols; D060890:B7-H1 Antigen / Q000037:antagonists & inhibitors*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000276:immunology*; D017321:Clinical Trials, Phase I as Topic; D006801:Humans; D017239:Paclitaxel / Q000627:therapeutic use; D061026:Programmed Cell Death 1 Receptor / Q000096:biosynthesis*; D064726:Triple Negative Breast Neoplasms / Q000188:drug therapy / Q000276:immunology
chemical_list: C520255:130-nm albumin-bound paclitaxel; D000418:Albumins; D060890:B7-H1 Antigen; C423236:CD274 protein, human; D061026:Programmed Cell Death 1 Receptor; D017239:Paclitaxel