Immunotherapy in primary hormone-receptor positive breast cancer: A systematic review

Hormone-receptor positive (HR+), HER2 negative breast cancer (BC) is considered immunologically silent, thus investigation of immunotherapy in this subtype has evolved slower. This systematic review offers an overview of the clinical trials investigating the safety and efficacy of ICI in primary HR+ /HER2- BC. Literature search was conducted up to October 30, 2022 to identify immunotherapy trials with checkpoint inhibitors in non-metastatic HR+ /HER2- breast cancer. 39 trials were identified, mainly in early-phase clinical trials. None of the trials investigate ICI monotherapy and only 2 Phase 3 clinical trials are ongoing. Most trials investigate the use of ICI in the neoadjuvant setting in combination with chemotherapy. 18 trials have reported results and 6 of them efficacy results specifically for HR+ /HER2- BC. ICI could be a promising therapeutic strategy for HR+ /HER2- BC, however clinical benefit is restricted to subgroups of patients, depending on tumor molecular profile.