Mechanisms linking obesity, inflammation and altered metabolism to colon carcinogenesis.

Due to its prevalence, obesity is now considered a global epidemic. It is linked to increased risk of colorectal cancer, the third most common cancer and the second leading cause of death among adults in Western countries. Obese adipose tissue differs from lean adipose tissue in its immunogenic profile, body fat distribution and metabolic profile. Obese adipose tissue releases free fatty acids, adipokines and many pro-inflammatory chemokines. These factors are known to play a key role in regulating malignant transformation and cancer progression. Obese adipose tissue is infiltrated by macrophages that participate in inflammatory pathways activated within the tissue. Adipose tissue macrophages consist of two different phenotypes. M1 macrophages reside in obese adipose tissue and produce pro-inflammatory cytokines, and M2 macrophages reside in lean adipose tissue and produce anti-inflammatory cytokines, such as interleukin-10 (IL-10). The metabolic networks that confer tumour cells with their oncogenic properties, such as increased proliferation and the ability to avoid apoptosis are still not well understood. We review the interactions between adipocytes and immune cells that may alter the metabolism towards promotion of colorectal cancer.