The immunologic aspects in hormone receptor positive breast cancer.

Background: Although hormone receptor positive/HER2-negative (HR +/HER2-) breast cancer is the most diagnosed breast cancer type, the immunologic aspects HR positive breast cancer (BC) has been neglected until recently.  The purpose of this paper is to review the current knowledge of the immune environment in HR positive BC and the potential use of immunotherapy in these patients.

Method: A computer-based literature research was carried out using PubMed, American Society of Clinical Oncology Annual Meeting (ASCO) and San Antonio Breast Cancer Symposium (SABCS).

Results: The tumour microenvironment (TME), with infiltrating immune cells, plays an important role in HR positive BC. However, the effects of these immune cells are different in the luminal cancers compared to the other breast cancer types. Even though PD-1 and PD-L1 are less expressed in HR positive BC, pathological complete response (pCR) was more often seen after PD-1 inhibitor treatment in patients with an increased expression. The studies support the assertion that endocrine therapy has immunomodulatory effect.

Conclusion: The reviewed literature indicates that immune cells play an important role in HR positive BC. Considerably more research is needed to determine the real effect of the TME in this patient group.