The Dark Knight: Functional Reprogramming of Neutrophils in the Pathogenesis of Colitis-Associated Cancer

Neutrophils are the primary myeloid cells that are recruited to inflamed tissues, and they are key players during colitis, being also present within the tumor microenvironment during the initiation and growth of colon cancer. Neutrophils fundamentally serve to protect the host against microorganism invasion, but during cancer development, they can become protumoral and lead to tumor initiation, growth, and eventually, metastasis-hence, playing a dichotomic role for the host. Protumoral neutrophils in cancer patients can be immunosuppressive and serve as markers for disease progression but their characteristics are not fully defined. In this review, we explore the current knowledge on how neutrophils in the gut fluctuate between an inflammatory or immunosuppressive state and how they contribute to tumor development. We describe neutrophils' antitumoral and protumoral effects during inflammatory bowel diseases and highlight their capacity to provoke the advent of inflammation-driven colorectal cancer. We present the functional ambivalence of the neutrophil populations within the colon tumor microenvironment, which can be potentially exploited to establish therapies that will prevent, or even reverse, inflammation-dependent colon cancer incidence in high-risk patients.