Colorectal Cancer, from the CureRays guide library.

Colorectal cancer starts in the colon or rectum, usually from a small growth called a polyp; screening can catch and remove polyps before they ever become cancer.

What it is.

The colon and rectum form the last several feet of the digestive tract, absorbing water and storing waste. Most colorectal cancers begin as a polyp — a small growth on the inner lining — that slowly turns cancerous over years. Because that change is slow, screening (like a colonoscopy) can find and remove polyps before cancer ever develops, or catch cancer early when it is highly curable. Where the tumor sits matters: rectal cancers are low in the pelvis and often involve radiation, while colon cancers higher up usually do not.

How radiation treats it.

Radiation uses focused high-energy x-rays to damage cancer-cell DNA so the cells can no longer divide. Healthy cells repair this damage better than cancer cells, so fractionated treatment clears cancer while sparing normal tissue. For rectal cancer, modern image-guided techniques aim the dose tightly to protect the bladder, small bowel, and surrounding organs. Sessions are painless and brief; side effects can include temporary loose stools, mild skin irritation, and fatigue that settle after treatment.

The ways we can treat it.

Neoadjuvant chemoradiation (rectal). Combines daily radiation over about 5 weeks with chemotherapy before surgery to shrink the tumor and dramatically reduce local recurrence.

Short-course radiation (rectal). A faster five-day radiation schedule, often as part of 'total neoadjuvant therapy,' that is more convenient and equally effective for suitable patients.

SBRT for oligometastases. Precise high-dose radiation can ablate a small number of spots in the liver or lung when colorectal cancer spreads to only a few places.

Questions we hear often.

Will I need a permanent colostomy bag? Most people do not. Modern surgery preserves bowel function for the majority; a permanent bag is needed only in select low rectal tumors, and your team will discuss this in advance.

Does colon cancer need radiation? Usually no — colon cancer is treated with surgery and sometimes chemo. Radiation is mainly used for rectal cancer because of its location in the pelvis.

When should I get screened? At average risk, start at age 45. Screening can remove polyps before they turn into cancer, making it one of the most effective cancer-prevention tools we have.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.