Colon polyp size and cancer risk

Cancer occurs when cells grow out of control, creating tumours. Colon cancer is no exception.

Colon Cancer usually starts with atypical growth in the colon. Doctors call these growths polyps. Not all polyps are cancerous. However, having a polyp is a risk factor for eventually developing cancer.

At least 95% colon cancers start with polyps. It can take years for these polyps to turn into cancer. This is why colon cancer screenings are so effective in preventing cancer before it spreads.

Doctors divide colon polyps into several subtypes:

• tubular: a tube-shaped projection
• villous: a finger-like projection

Both can be cancerous or precancerous, but large growths are more likely to be villous.

An adenoma is a colon polyp that can turn into cancer.

There is no fixed size at which a polyp will become cancerous, nor any particular size that is always cancerous. Even among large polyps, the majority are not cancerous.

A study 2018 size of polyps and cancer included 550,811 polyps. The majority (81%) had a diameter of 1 to 9 mm. Only a small percentage of polyps (3.4%) were cancerous.

However, cancer rates were highest among the largest polyps.

The percentage of cancerous polyps, by size, was as follows:

A study 2018 in China correlated polyps larger than 31 mm with a higher risk of colon cancer. People over 50 were more likely to get cancer and polyps, especially large polyps.

Another study 2018 supports this finding. The study analyzed a total of 15,906 polyps. Among polyps larger than 30 mm, 4.6% were cancerous. Cancer incidence in polyps less than 5 mm was 0%.

Colon polyps grow slowly, and people with polyps or colon cancer may not have any symptoms. This is why colon cancer screenings are so important.

People with symptoms can experience:

• rectal bleeding
• bleeding during a bowel movement
• feeling like their bowels aren’t empty after a bowel movement
• frequent constipation or diarrhea
• stomach pain
• changes in bowel habits

A doctor can usually remove colon polyps at the same time as when they detect them.

During a polypectomy, a doctor removes the polyp. This allows them to test the polyp for cancer and prevent noncancerous and precancerous polyps from growing and turning into cancer.

Depending on the number and size of the polyps, a doctor may recommend additional or more frequent colon cancer screenings.

If the polyps are cancerous, a doctor may recommend surgical resection. This involves the removal of part of the colon to prevent the cancer from continuing to grow.

Most early-stage cancers do not require chemotherapy if a doctor is able to remove the cancer. However, more advanced stages may require chemotherapy.

Some types of colon cancer respond to targeted immunotherapy drugs. Immunotherapy helps the immune system recognize and treat cancer. The right treatment depends on:

• cancer itself
• the health of the person with cancer
• how advanced is the cancer
• whether it has spread to other parts of the body

The good treatment too depend on the unique characteristics of cancer, which experts call histology. Treatment will also depend on whether or not the cancer has certain mutations.

Early removal of colon polyps has good prospects. However, people with a history of polyps may develop more polyps.

Certain conditions, such as intestinal polyposis, can increase a person’s risk of developing more polyps. A person with these conditions has a higher lifetime risk of colon cancer and may need more frequent screenings.

Lynch syndrome or familial adenomatous polyposis (FAP) are genetic predispositions that increase the risk for these cancers.

About half of people with colorectal cancer develop cancer that spreads, usually to the liver. Once colorectal cancer has spread, the outlook is less favorable, with most people only living 5 or 6 months.

However, in the early stages, if a doctor is able to remove the cancer completely, the outlook is good and it may be possible to cure the cancer. A person may need ongoing cancer screenings for the rest of their life.

Many people can avoid or delay a colonoscopy. However, it remains a very effective tool for detecting colon polyps and early stages of colon cancer.

These polyps usually grow slowly, allowing plenty of time for detection and removal before they turn cancerous. Without screening, they can go undetected, giving the cancer time to grow and spread.

It is much easier to treat polyps and cancer at an early stage than to treat advanced colon cancer. People over 50, as well as people at high risk for colon cancer, should discuss screening with a doctor.

People should also note that there are other colon cancer screening options.

Learn more about colon cancer screening here.