Abstract MS1-2: MS1-2 Breast cancer immunotherapy: Building on clinical success

Abstract

Abstract Breast cancer has long been considered immunologically silent, but it is now clear that the immune system is active in this disease. Breast cancers can naturally induce tumor infiltrating lymphocytes (TIL), which represent a biomarker of the endogenous immune response. Increasing data support the association of TIL with a better prognosis for breast cancer patients, and also suggest that the presence of TIL can predict response to standard breast cancer therapies. These observations have stimulated intense interest in harnessing the natural breast cancer-specific immune response for therapeutic benefit. Breast cancer vaccines that activate the breast cancer-specific immune response have been tested for many years, with minimal clinical success to date. This is likely due to both inadequate vaccination platforms and dominant mechanisms of immune suppression active within the breast tumor microenvironment. In the tumor microenvironment, the immune checkpoint pathway governed by the programmed cell death-1 (PD-1) receptor and its ligand PD-L1 has emerged as a significant mechanism of immune resistance in a variety of cancers, including breast cancer. Several monoclonal antibody antagonists of PD-1 or PD-L1 unleash the activity of tumor-specific T cells in multiple types of cancer, resulting in durable clinical responses that translate into an overall survival benefit. Early data in breast cancer reveal that these agents have activity in some patients with triple negative and estrogen receptor-positive breast cancer, with response rates that range from about 5-44%. Antagonists of the PD-1 pathway are typically well-tolerated in breast cancer patients, with unique immune-related adverse events that are quite manageable. Selecting patients for PD-L1 expression appears to enrich for responders to single agent therapies that target PD-1/PD-L1. Based on early clinical data, agents that target the PD-1 pathway are under accelerated clinical development for breast cancer treatment. The challenge moving forward is converting immunotherapy non-responders to responders. Combination immunotherapies that integrate standard breast cancer therapies and/or multiple innovative immune-based therapies to simultaneously promote T cell activity and relieve multiple mechanisms of immune suppression at the tumor site have the greatest potential for enhancing the clinical activity of immunotherapy for breast cancer patients. Citation Format: Emens LA. MS1-2 Breast cancer immunotherapy: Building on clinical success [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr MS1-2.