**3.2 Colorectal carcinoma**

Colorectal carcinoma is among the top five most common malignancies worldwide. The common sites involved in colon cancer are the rectosigmoid area, caecum and the transverse colon. The majority (>90%) of colorectal cancers are sporadic. The development of sporadic colorectal cancer is preceded by an adenomatous polyp, the so-called adenoma-carcinoma sequence. Colonocytes rely on nutrients derived from the fermentation of indigestible fibers by resident bacteria. Some sporadic cancers are associated with dysbiosis [69, 70]. Abnormalities of Paneth cells, including metaplasia, have been reported in colorectal cancer [62]. Furthermore, Paneth cells in the colon of patients diagnosed with adenomatous polyps or invasive cancer are associated with aggressive disease and poor prognosis [70].
