The genomic landscape of breast cancer and its interaction with host immunity.

Molecular profiling of thousands of primary breast cancers has uncovered remarkable genomic diversity between breast cancer subtypes, and even within subtypes. Only a few driver genes are recurrently altered at high frequency highlighting great challenges for precision medicine. Considerable evidence also confirms the role of host immunosurveillance in influencing response to therapy and prognosis in HER2+ and triple negative breast cancer. The role of immunosurveillance in ER + disease remains unclear. Advances in both these fields have lead to intensified interest in the interaction between genomic landscapes and host anti-tumour immune responses in breast cancer. In this review, we discuss the potential genomic determinants of host anti-tumour immunity - mutational load, driver alterations, mutational processes and neoantigens - and their relationship with immunity in breast cancer. Significant differences exist in both the genomic and immune characteristics amongst breast cancer subtypes. While ER + disease appears to be less immunogenic than HER2+ and triple negative breast cancer, it displays the greatest degree of heterogeneity. Mutational and neoantigen load appears to incompletely explains immune responses in breast cancer. Driver alterations do not appear to increase immunogenicity. Instead, they could contribute to immune-evasion or an immunosuppressive microenvironment, and therefore represent potential therapeutic targets. Finally, we also discuss the tailoring of immunotherapeutic strategies by genomic alterations, with possible multimodal combination approaches to maximise clinical benefits.