Impact of systemic therapy on circulating leukocyte populations in patients with metastatic breast cancer

Tumors affect the immune system, locally and systemically. The frequencies of specific circulating immune cell populations correlate with disease progression as well as prognosis of the patients. Although largely neglected, conventional antitumoral therapies often possess immunomodulatory properties and affect the levels of specific immune cell populations. Most information, however, derive from animal or in vitro studies. As this could impact prognosis as well as response to therapy, further studies of the effects of treatment on circulating immune cells in patients are warranted. In this pilot study, we evaluated a wide panel of circulating immune cells over time (up to six months) in ten patients with metastatic breast cancer receiving standard antitumoral regimens. Overall, endocrine therapy tends to enrich for natural killer (NK) and natural killer T (NKT) cells in the circulation, whereas both chemotherapy and endocrine therapy reduce the levels of circulating monocytic myeloid-derived suppressor cells (Mo-MDSCs). This indicates that the systemic immunosuppressive profile observed in patients tends to revert over the course of systemic therapy and holds promise for future combination treatment with standard antitumoral agents and immunotherapy.