New insights into the role of complement system in colorectal cancer (Review)

Colorectal cancer (CRC) is one of the most common cancers worldwide. With the growing understanding of immune regulation in tumors, the complement system has been recognized as a key regulator of tumor immunity. Traditionally, the complement cascade, considered an evolutionarily conserved defense mechanism against invading pathogens, has been viewed as a crucial inhibitor of tumor progression. Complement components or activation products produced via cascade‑dependent or ‑independent processes are associated with the regulation of tumor‑associated inflammation. Various forms of complement activation products present in body fluids or inside cells, along with complement regulatory proteins and complement receptors, are involved in tumor cell growth and modulating the tumor microenvironment. In the present review, the role of the complement system in the tumor immunity of CRC is discussed. In addition, the contribution of the unconventional cascade‑independent pathway of complement activation in CRC progression is highlighted. A deeper understanding of the mechanism underlying the complement system in colitis‑associated colorectal cancer (CAC) may provide novel insights to assist the development of methods to prevent tumor progression and identify potential targets for the treatment of CAC.