US Trends

causes of rectal cancer

Rectal cancer develops when normal cells in the rectum gradually acquire genetic changes that make them grow out of control, and several well-known risk factors make these changes more likely.

Key idea: “Causes” vs “Risk factors”

Doctors usually talk about risk rather than a single direct cause.

Most rectal cancers are thought to result from a mix of:

  • Genetic changes in rectal cells (inherited or acquired over life).
  • Long‑term inflammation or damage to the bowel lining.
  • Lifestyle and environmental exposures that increase stress on these cells.

You can have risk factors and never get cancer, and you can get cancer without obvious risks, but these factors shift the odds.

1. Genetic and inherited factors

Some people are born with gene changes that strongly raise their risk:

  • Inherited syndromes
    • Lynch syndrome (hereditary nonpolyposis colorectal cancer, HNPCC) greatly increases the risk of colon and rectal cancer.
* Familial adenomatous polyposis (FAP) causes hundreds of polyps in the colon/rectum, many of which will turn cancerous if not treated.

* Together, inherited syndromes account for a small but important fraction (around 5%) of colorectal cancers.
  • Family history without a known syndrome
    • Having a parent, sibling, or child with colon or rectal cancer increases your own risk, even when no specific syndrome is identified.
  • Acquired gene mutations in rectal cells
    • Over many years (often 10–15), normal rectal lining can progress from normal tissue → polyp → cancer as mutations accumulate.
* Commonly affected genes include APC, KRAS, and the tumor‑suppressor gene p53, which regulate cell growth and cell death.

2. Medical conditions involving the bowel

Several diseases affecting the colon/rectum raise rectal cancer risk:

  • Inflammatory bowel disease (IBD)
    • Long‑standing ulcerative colitis or Crohn’s disease involving the colon/rectum significantly increases colorectal cancer risk, especially after many years of inflammation.
  • Polyps and previous colorectal cancers
    • Adenomatous polyps (precancerous growths) in the colon or rectum can gradually become malignant if not removed.
* A past history of colon, rectal, or anal cancer increases the chance of developing another colorectal cancer.
  • Other cancers and treatments
    • Prior radiation therapy directed at the abdomen or pelvis (for example, for another cancer) can raise later colorectal cancer risk.
* Some people with ovarian cancer or other abdominal cancers have higher colorectal risk, sometimes due to shared genetic factors.

3. Lifestyle and environmental risk factors

These factors don’t guarantee cancer, but they are consistently linked to higher rectal/colorectal cancer rates:

  • Diet
    • A pattern of eating high in red and processed meats and low in vegetables, fruits, and fiber is associated with increased rectal cancer risk.
* Charred or heavily grilled meats may also contribute, according to some research.
  • Physical inactivity
    • Regular exercise appears protective, while a sedentary lifestyle increases risk.
  • Obesity and metabolic health
    • Excess body weight, especially around the waist, is linked to higher rectal/colorectal cancer risk.
* Poorly controlled type 2 diabetes is also associated with increased risk.
  • Smoking
    • Smoking is a strong risk factor for many cancers, including colorectal cancer; smokers have a substantially higher chance of developing and dying from these cancers.
  • Alcohol
    • Heavy alcohol intake (for example, three or more drinks per day) is linked to increased rectal/colorectal cancer risk.

4. Age, sex, and other non‑modifiable risks

Some factors you cannot change but that matter for risk and screening decisions:

  • Age
    • Most rectal cancers are diagnosed after age 50, though cases in younger adults have been rising in recent years.
  • Sex and general colorectal risk
    • Colon and rectal cancers together are among the most common cancers and leading causes of cancer death worldwide.
  • Radiation exposure
    • As noted above, prior pelvic or abdominal radiation for another condition increases later colorectal cancer risk.

5. “Latest news” and trends you might see

In recent years, several trends around rectal and colorectal cancer have been discussed a lot:

  • Rising cases in younger adults (often under 50), leading many organizations to recommend starting routine colorectal screening at age 45 instead of 50.
  • Ongoing research on gut microbiome, ultra‑processed foods, and sedentary digital lifestyles as possible additional contributors, though these links are still being clarified.
  • Expanded use of genetic testing for Lynch syndrome and FAP in families with multiple colorectal cancers, so high‑risk people can be screened earlier and more intensively.

6. Practical takeaways and when to act

If you’re worried about the causes of rectal cancer, the most actionable steps usually involve:

  • Not smoking, and seeking help to quit if you do.
  • Limiting alcohol, ideally staying below heavy‑drinking levels.
  • Eating more fiber‑rich plant foods and less red/processed meat.
  • Staying physically active and maintaining a healthy weight.
  • Getting recommended colorectal screening (colonoscopy or other tests), especially if you are over 45 or have risk factors or family history.

If you have symptoms such as rectal bleeding, a persistent change in bowel habits, unexplained weight loss, or abdominal pain, or if you have a strong family history, it is important to see a doctor or gastroenterologist promptly for individualized advice and possible testing.

Information gathered from public forums or data available on the internet and portrayed here.