Overview & Definition

Colon cancer (a major part of colorectal cancer) occurs when cells in the colon begin to grow uncontrollably. It often starts as benign polyps on the inner lining that can become cancer over time. Detecting and removing polyps early prevents most colon cancers.

How Colon Cancer Starts

Most cases arise from adenomatous polyps over many years through genetic changes (e.g., APC, KRAS, TP53, mismatch-repair genes). Hereditary syndromes like Lynch syndrome and FAP increase risk.

Risk Factors

• Age (most after 50, but rising in younger adults)
• Family history and inherited syndromes
• Diet & lifestyle (low fiber, high red/processed meat, obesity, inactivity, alcohol, smoking)
• Inflammatory bowel disease (ulcerative colitis, Crohn’s)
• Type 2 diabetes (in some studies)

Regular screening reduces risk and catches disease early.

Signs & Symptoms

• Changes in bowel habits or stool caliber
• Blood in stool or rectal bleeding
• Abdominal pain, cramping, bloating
• Feeling of incomplete evacuation
• Unexplained anemia, fatigue, weight loss

Screening & Prevention

Begin at age 45 for most adults (earlier with risks). Options:

• Colonoscopy (detects & removes polyps)
• Stool tests (FIT/FOBT; FIT-DNA)
• Sigmoidoscopy or CT colonography

Diagnosis & Staging

Treatment Options

• Surgery (segmental colectomy) for early stages
• Chemotherapy (e.g., FOLFOX, CAPOX, FOLFIRI)
• Targeted therapy (anti-VEGF, anti-EGFR in RAS-wild type)
• Immunotherapy for dMMR/MSI-H tumors
• Radiation (more common in rectal cancer; selective use in colon)

Prognosis

Localized disease is highly treatable; five-year survival exceeds 90% when detected early. Stage and tumor biology influence outcomes.

Sources & Attribution

• NCI — Colorectal Cancer: cancer.gov/types/colorectal
• CDC — Colorectal Cancer: cdc.gov/colorectal-cancer
• MedlinePlus — Colon Cancer: medlineplus.gov/coloncancer.html

Educational only; not medical advice.