Colorectal Cancer
A malignancy that arises through a stepwise accumulation of mutations turning benign adenomatous polyps into invasive carcinoma, so screening and symptoms both follow directly from where in the bowel that clone happens to grow.
First principles
Cancer arises through the adenoma-carcinoma sequence, not in one step
Colorectal cancer almost always begins as a benign adenomatous polyp. Sequential mutations (classically inactivating APC, then activating KRAS, then losing p53) progressively deregulate cell growth, so the polyp accumulates dysplasia and eventually breaches the basement membrane to become invasive carcinoma. Because this takes years, there is a long window in which removing a polyp at colonoscopy prevents the cancer that would otherwise have formed, which is the entire rationale for bowel screening and polypectomy.
Educational content pending clinical review. Not medical advice.