The future of breast cancer systemic therapy: the next 10 years.

Over the past 50 years, substantial progress has been made in the systemic treatment of early-stage and advanced breast cancer. The use of chemotherapy in the adjuvant and metastatic settings has demonstrated proven efficacy and it has been clearly demonstrated that targeting the estrogen receptor and human growth factor receptor 2 (HER2) is efficacious in early and advanced disease. Despite these advances, vexing clinical challenges remain particularly related to the treatment of triple-negative breast cancer (TNBC; estrogen receptor [ER]-negative, progesterone receptor [PR]-negative, and HER2-negative) where little progress has been made therapeutically in more than a decade. While recurrences of hormone-responsive breast cancer are overall less common, late relapses after cessation of endocrine therapy are a more frequent occurrence in modern times and reflect the problem of underlying tumor dormancy that as yet has not been overcome. Multiple molecular tools are now available to interrogate the biology of breast cancer, though exactly how to make this information meaningful in the clinic has proven challenging, and molecularly driven clinical trials have faced feasibility challenges. In parallel, focus has expanded from tumor to host with the ability to ascertain underlying germline alterations, such as inherited BRCA1 and BRCA2 mutations, which may be responsible for breast cancer carcinogenesis and, importantly, may have implications for treatment. These clinical advances in germline genetics, made possible by both scientific investigation as well as the courts, still face challenges related to increasing encounters with variants of unknown significance and difficulty in predicting risks associated with less well-characterized inherited cancer predisposition syndromes. In this paper, we attempt to predict the next 10 years of breast cancer, in particular focusing on how the past serves as prologue to the future in this disease.