Inflammation and Cancer: A Temporal Perspective on Emerging Cellular and Molecular Mechanisms, Focusing on Gastrointestinal Cancers

Gastrointestinal (GI) cancers are the most common causes of global cancer burden and cancer-related deaths. Chronic inflammation is a hallmark feature of GI tumors and plays an important role in tumor initiation, progression, and therapeutic response. The genetic makeup of cancer cell, as well as epigenetic alterations, and biological processes constitute an inflammatory tumor microenvironment (TME) that provides an essential nich for cancer initiation and progression. Cancer-associated inflammation, a key component of TME, displays protumoral or antitumoral activity depending on the composition, spatial distribution, and functional status of the immune cells involved, thus adversely affecting response to cancer treatment and clinical outcomes, whereas acute inflammation supports T-cell priming, activation, and infiltration into malignant tissues, thereby conferring anti-tumoral immunity. Inflammatory cells and proinflammatory molecules within the TME act as a bridge between inflammation and cancer. The majority of cells involved in the inflammatory process in the TME are innate immune cells, which play a critical role in shapping both the cellular composition of the TME and the plasticity of cancer cells and stromal cells. Activation of innate immune cells in the TME initiates the production of inflammatory, regenerative, and anti-inflammatory soluble molecules, resulting in adaptive immune response to the cancer. Additionally, aberrant activation of intracellular signaling pathways, inflammatory molecules, and metabolites have critical roles in the development and healing of inflammation during carcinogenesis. Cancer-associated inflammation may inhibit the effectiveness of anti-cancer agents by causing enzymatic degradation of drugs and modulating the immun activity, thus affecting survival of patient. In this review article, we highlight the genetic and cellular mechanisms involved in the formation of the inflammatory component of the TME in GI cancers, the soluble molecules, the cancer cell-immune cell interactions, and the implications of all these for clinical outcomes. We also comprehensively address the mechanisms linking chronic inflammation to cancer, with a focus on the most frequent GI cancers.