Colorectal Cancer

Colorectal cancer begins in the colon (large intestine) or rectum. Most colorectal cancers start as polyps—abnormal growths on the inner lining—that can slowly develop into cancer over 10-15 years. This is why screening to find and remove polyps can prevent cancer. **Types:** - **Adenocarcinomas:** About 96% of colorectal cancers. Starts in cells that make mucus. - **Carcinoid tumors:** Start in hormone-making cells - **Gastrointestinal stromal tumors (GISTs):** Start in cells in the wall of the colon - **Lymphomas:** Cancer of immune system cells **Stages:** - Stage 0: Cancer only in innermost lining (carcinoma in situ) - Stage I: Cancer grown into layers of colon wall - Stage II: Cancer through colon wall but not to lymph nodes - Stage III: Cancer spread to nearby lymph nodes - Stage IV: Cancer spread to distant organs (liver, lungs) **Key Point:** Colorectal cancer is one of the most preventable cancers. Screening can find and remove polyps before they become cancer, and early-stage cancer is highly curable.

**Polyp Development:** Most colorectal cancers develop from polyps over 10-15 years. Not all polyps become cancer, but adenomatous polyps (adenomas) have the highest risk. Removing polyps during colonoscopy prevents cancer. **Genetic Factors:** About 5-10% of colorectal cancers are caused by inherited gene mutations. Lynch syndrome (hereditary nonpolyposis colorectal cancer) and familial adenomatous polyposis (FAP) significantly increase risk. **Diet and Lifestyle:** Diets high in red and processed meats and low in fiber increase risk. Obesity, physical inactivity, smoking, and heavy alcohol use are all risk factors. **Inflammatory Bowel Disease:** Long-standing ulcerative colitis or Crohn's disease of the colon increases colorectal cancer risk, requiring more frequent screening. **Rising Rates in Young People:** Colorectal cancer is increasing in people under 50 for unclear reasons. This has led to screening recommendations starting at age 45 rather than 50.