Colorectal Cancer

What it is

Overview

Colorectal cancer (CRC) is the third most common cancer in both men and women. It begins in the inner lining of the colon or rectum. Most cases develop from polyps — small growths inside the colon — which is why colonoscopy screening is so powerful: finding and removing polyps prevents cancer before it starts. Rates are rising alarmingly in adults under 50.

Biology

How It Develops

Most CRCs develop from adenomatous polyps over 10–15 years. Mutations accumulate in the APC tumor suppressor gene and later in KRAS, TP53, and other genes, transforming normal colon cells into cancer. Inflammatory bowel disease accelerates this process, and Lynch syndrome (inherited mismatch repair deficiency) dramatically increases lifetime risk.

Warning signs

Symptoms

• —Change in bowel habits (diarrhea, constipation, narrowing of stool)
• —Rectal bleeding or blood in stool
• —Persistent abdominal cramping or pain
• —Feeling that the bowel doesn't fully empty
• —Weakness, fatigue, or unexplained weight loss

Detection

Diagnosis Methods

• —Colonoscopy (gold standard)
• —Sigmoidoscopy
• —Stool DNA test (Cologuard)
• —Fecal immunochemical test (FIT)
• —CT colonography
• —CT scan, MRI, and PET for staging

Medical care

Treatment Options

• —Surgery (colectomy, colostomy if needed)
• —Radiation therapy (mainly for rectal cancer)
• —Chemotherapy (FOLFOX, FOLFIRI)
• —Targeted therapy (bevacizumab, cetuximab)
• —Immunotherapy (for MSI-H/dMMR tumors)

Data

Statistics

Prevention

Risk Factors

• —Age over 50 (but rates rising in younger adults)
• —Personal or family history of colorectal cancer or polyps
• —Inflammatory bowel disease (Crohn's, ulcerative colitis)
• —Lynch syndrome or familial adenomatous polyposis (FAP)
• —High-fat, low-fiber diet; red and processed meat
• —Obesity, physical inactivity, smoking, heavy alcohol use

Further reading

Resources