Institute of Human Anatomy on Instagram: "How Colon Cancer Actually Starts: From Polyp to Metastasis Looking at real human colon tissue to understand the progression of colorectal cancer - one of the most preventable cancers if caught early. THE STARTING POINT: Cancer begins in the tunica mucosa - the inside lining of the colon you can see here. Genetic mutations trigger abnormal cell growth in epithelial cells. THE POLYP STAGE: These mutations first create small, non-cancerous growths called po