The inflammation during colorectal cancer: A friend or a foe?

Abstract In the past two decades, a close relationship between inflammation and carcinogenesis has been described. In fact, since 2011, the inflammation has been considered as one of the ten hallmarks of cancer. However, natural selection did not evolve inflammation to cause troubles and diseases to our body. Both types of inflammation, acute and chronic, are natural events orchestrated by the immune system to generate protection against infectious and noninfectious insults, including colorectal cancer (CRC). Strong evidence in humans and some animal models of CRC indicates that the absence of molecules associated with inflammation induces an increased number of tumors and a reduction in apoptosis, suggesting that inflammation is involved in protection when the tumor has been established. However, another line of evidence, also well supported, suggests that the inflammatory processes during cancer development, especially in CRC, are very undesirable because it accelerates the tumor growth in many cases. Therefore, many questions arise regarding the relationship between inflammation and CRC: What are the steps and decisions taken by the immune system to guide the inflammation to favor CRC development? Or maybe, is the inflammation a process involved in protection against CRC establishment? The balance between the inflammation, their causes and checkpoints is extremely important during CRC development, and there are studies looking to solve these questions. In this chapter, we try to establish some of the stronger proofs suggesting a major role for inflammation in the protection during early CRC development. The understanding of the complex relationship between inflammation and cancer may help to develop combinatory therapies (drugs and immunomodulators) to blockade the possible collateral damage induced by chronic inflammation that favors CRC elimination.