Always look on the bright side: Anti-tumor functions of neutrophils

Neutrophils are the most abundant population of white blood cells in the human circulation playing a critical role in inflammation and in host defense against microbial infections. In recent years there has been growing interest in understanding the role the tumor microenvironment plays in tumor growth and progression. In this context, the role neutrophils play has been a matter of debate as neutrophils were shown to possess both tumor promoting and tumor limiting properties. These conflicting observations stem from differences in how neutrophils respond to environmental cues as well as from the existence of distinct tumor-promoting and tumor-limiting neutrophil populations. Here, we review general aspects of neutrophil biology and the favorable functions of neutrophils in the primary tumor and the pre-metastatic microenvironment. We further discuss the mechanisms neutrophils employ to limit tumor progression and highlight the aspects of neutrophil biology that may be targeted in future neutrophil-based cancer immunotherapies.