Targeting Myeloid Determinants of Breast Cancer

Breast cancer (BC) is the most commonly diagnosed cancer in women worldwide and the second largest cause of cancer-related deaths. Recently, numerous agents, including inhibitors targeting CDK4/6, PARP, and immune checkpoint molecules, have been clinically developed as molecular targeted therapy in the treatment of BC. However, these treatments are applicable to a limited type of BC, and are effective in only a small proportion of the treated patients, or recurrence and metastasis frequently occur in the treated patients even if receiving the treatments and effective initially. This is because tumor cells evolutionally change through the interplay with numerous components in the host, and the consequent increase of heterogeneity and complexity of both tumor cells and host environment profoundly impacts on the therapeutic efficacy. The immune system is the most influential factor in their reciprocal evolution, and the better management may be the key to successful cancer treatment. In the human immune system, myeloid cell population is the major cellular component, and its abnormality could thoroughly impact on the whole body potentially leading to treatment resistance of cancer. Thus, a deeper understanding of this large myeloid cell population may lead to successful immune control in the treatment of a broader range of types of BC, including not only TNBC but also other types. Here, we provide a recent overview of various myeloid populations in association with BC, and possible treatments that may be able to inhibit or eliminate the myeloid-derived vicious factors.