In most cases, no. Your doctor can't usually tell, simply by looking at a polyp during a colonoscopy, if it's cancerous. But if a polyp is found during your colonoscopy, your doctor will remove it and send it to a lab for a biopsy to check for cancerous or precancerous cells.
A gastroenterologist, the specialist who usually performs a colonoscopy, can't tell for certain if a colon polyp is precancerous or cancerous until it's removed and examined under a microscope.
The doctor will then send any removed polyps to a pathologist for a biopsy to see if cancer is present. If the biopsy reveals that cancer is present, then cancer specialists will outline a treatment plan for the person. Common treatments for colon cancer include surgery, chemotherapy, and radiotherapy.
Most polyps are benign (not cancerous). Your doctor can tell if a colon polyp is cancerous during a colonoscopy by collecting tissue to biopsy. The results of the biopsy are typically sent to your doctor within a week. Only 5% to 10% of all polyps become cancerous.
How long does it take for a polyp to turn into cancer? The growth and mutation of colon polyps into cancer is a slow process, taking an estimated 10 years on average. So as long as patients are screened, it is unlikely they will develop cancerous polyps.
Most polyps grow slowly and take from between 10 and 15 years to become cancerous.
Depending on their size and location in the colon, serrated polyps may become cancerous. Small, serrated polyps in the lower colon, also known as hyperplastic polyps, are rarely malignant. Larger serrated polyps, which are typically flat (sessile), difficult to detect and located in the upper colon, are precancerous.
If the colonoscopy finds one or two small polyps (5 mm in diameter or smaller), you are considered at relatively low risk. Most people will not have to return for a follow-up colonoscopy for at least five years, and possibly longer.
If your doctor finds one or two polyps less than 0.4 inch (1 centimeter) in diameter, he or she may recommend a repeat colonoscopy in 7 to 10 years, depending on your other risk factors for colon cancer. Your doctor will recommend another colonoscopy sooner if you have: More than two polyps.
“After an advanced polyp has been removed, the whole colon remains at risk for cancer, and periodic colonoscopy is needed,” said Schoen. Intriguingly, the study also showed that people with non-advanced polyps had a risk for cancer similar to a person without polyps.
Polyps are common in American adults, and while many colon polyps are harmless, over time, some polyps could develop into colon cancer. While the majority of colon cancers start as polyps, only 5-10% of all polyps will become cancerous.
Before you go home, your doctor tells you if they removed any growths (polyps) or tissue samples (biopsies) from your bowel. The biopsy results can take up to 2 weeks. Your specialist writes to you with the results. If your GP referred you for the test, they should also receive a copy.
Right-sided polyps are more likely to develop into cancers — which often grow rapidly and have a higher risk for metastasis, spreading to distant body areas. Right-sided colon cancers also tend to develop from flat polyps rather than the usual mushroom-shaped ones, and are genetically atypical, too.
"Precancerous polyps are extremely common," he says. "We expect to find them in more than a quarter of the colonoscopies that we do at a minimum. So, you know, maybe a third or even a half of all patients getting [a] colonoscopy will have precancerous polyps."
Approximately 1% of polyps with a diameter less than 1 centimeter (cm) are cancerous. More than one polyp or a polyp that is 1 cm or bigger places you at higher risk for colon cancer. Up to 50% of polyps greater than 2 cm (about the diameter of a nickel) are cancerous.
A precancerous polyp by itself is not malignant but if left untreated can become cancerous. It is very common for adults to have polyps in their colon. Precancerous lesions can usually be surgically extracted to avoid cancer. There are two types of polyps hyperplastic polyps and adenomatous polyps.
Cancerous polyps tend to grow slowly. It is estimated that the polyp dwell time, the time needed for a small adenoma to transform into a cancer, may be on average 10 years (17).
Polypectomy. In the early stage when they are smaller, polyps can be removed by putting a tube with a tool in the rectum and cutting the cancer out. Minimally invasive surgery. Polyps that are too large or that can't be removed safely during screening are usually removed surgically.
The three different polyps are villous, tubular and tubulovillous. Adenomatous polyps will gradually show dysplastic changes, which differentiates them from hyperplastic polyps. In general, colonic polyps are benign but those that develop high-grade dysplasia will become malignant with time.
Studies show that few smaller polyps are cancerous. As polyps slowly grow, however, the cancer risk rises. It's estimated that it takes about 10 years for cancer to form into a colorectal polyp.
Once a colorectal polyp is completely removed, it rarely comes back. However, at least 30% of patients will develop new polyps after removal. For this reason, your physician will advise follow-up testing to look for new polyps. This is usually done 3 to 5 years after polyp removal.