Proteomic profiling of the autoimmune response to breast cancer antigens uncovers a suppressive effect of hormone therapy

Purpose: Proteomics technologies are well suited for harnessing the immune response to tumor antigens for diagnostic applications as in the case of breast cancer. We previously reported a substantial impact of hormone therapy (HT) on the proteome. Here, we investigated the effect of HT on the immune response toward breast tumor antigens. Experimental design: Plasmas collected 0-10 months prior to diagnosis of ER+ breast cancer from 190 postmenopausal women and 190 controls that participated in the Women's Health Initiative Observational Study were analyzed for the effect of HT on IgG reactivity against arrayed proteins from MCF-7 or SKBR3 breast cancer cell line lysates following extensive fractionation. Results: HT user cases exhibited significantly reduced autoantibody reactivity against arrayed proteins compared to cases who were Not Current users. An associated reduced level of IL-6 and other immune-related cytokines was observed among HT users relative to nonusers. Conclusion and clinical relevance: Our findings suggest occurrence of a global altered immune response to breast cancer-derived proteins associated with HT. Thus a full understanding of factors that modulate the immune response is necessary to translate autoantibody panels into clinical applications.