Targeting the host immune system: PD-1 and PD-L1 antibodies and breast cancerDawood, Shaheenah; Rugo, Hope S.Current Opinion in Supportive and Palliative Care: December 2016 - Volume 10 - Issue 4 - p 336–342 doi: 10.1097/SPC.0000000000000243 BONE AND HAEMATOLOGICAL PROBLEMS: Edited by Allan Lipton and James Berenson Buy Abstract Author InformationAuthors Article MetricsMetrics Purpose of review 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. Recent findings 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. Summary 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. aDepartment of Medical Oncology, Dubai Hospital, UAE bUniversity of California San Francisco Helen Diller Family Comprehensive Cancer Center, San Francisco, CA Correspondence to Dr Hope S. Rugo, MD, University of California San Francisco, 1600 Divisidero St., Box 1710, San Francisco, CA 94115, United States. Tel: +1 415 353 7618; e-mail: email@example.com Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved.