A colonoscopy is the primary procedure for screening and preventing colorectal cancer, allowing for the detection and removal of growths called polyps. A colon polyp is an abnormal cluster of cells forming on the lining of the colon or rectum. While nearly all colorectal cancers begin as a polyp, most polyps are benign and will never progress to cancer. During the procedure, a doctor can assess if a polyp is suspicious for malignancy based on its size and appearance. However, a doctor can never definitively confirm cancer at the time of the colonoscopy; only a laboratory analysis of the removed tissue can provide that final diagnosis.
Visual Clues That Raise Suspicion
Endoscopists use visual characteristics during the examination to assess the likelihood that a polyp is precancerous or malignant. The size of the growth is a primary factor, as polyps larger than 10 millimeters (one centimeter) carry a significantly higher risk of containing cancerous cells. The shape of the polyp also provides important clues about its potential for malignancy.
Polyps that have a stalk, known as pedunculated polyps, are generally considered lower risk than those without one. Sessile polyps, which lie flat against the colon wall, are more common and can be more concerning. Flat or depressed polyps are particularly worrisome because they can harbor deeper invasion even at a smaller size, making them easier to overlook.
The surface of the polyp is often examined using advanced imaging techniques. A smooth, uniform surface is reassuring, but an irregular, ulcerated, or friable (easily crumbled) texture is highly suspicious for a malignant change. Also, the pattern of blood vessels on the polyp’s surface can be analyzed, where a disorganized, disrupted, or missing vessel structure is a strong indicator of advanced tissue changes.
The Definitive Role of Pathology
While visual inspection provides a strong indication of a polyp’s risk, it is merely a guide for the endoscopist’s immediate action. The only way to know with certainty whether a polyp is cancerous is through a process called histopathological examination. This process begins immediately after the polyp is removed when it is sent to a pathology laboratory for detailed analysis.
A pathologist, a doctor who specializes in examining tissue samples, prepares the polyp and views thin slices of it under a powerful microscope. They look for specific cellular features that define cancer, such as disorganized cell growth, abnormal cell shapes, and enlarged nuclei. The pathologist also determines the extent of cell abnormality, classifying it as low-grade or high-grade dysplasia.
A primary finding is whether the malignant cells have invaded the submucosa, the layer beneath the inner lining of the colon. If the cancer cells are confined to the inner lining, it is considered non-invasive high-grade neoplasia, and the polypectomy is usually curative. If the cancer has spread into the submucosa, the polyp is classified as a malignant polyp (T1 cancer). This carries a risk of spreading to lymph nodes and may require further surgical treatment.
Polyp Classification and Removal Techniques
Polyps are categorized based on their cellular makeup, which directly relates to their potential to become cancerous. Adenomas are the most common type of precancerous polyp, accounting for the vast majority of colorectal cancers.
Within the adenoma category:
- Tubular adenomas are the least aggressive.
- Villous adenomas and tubulovillous adenomas are typically larger and carry a higher risk of high-grade dysplasia.
Other types include hyperplastic polyps, which are generally benign and low-risk, and sessile serrated lesions (SSLs), which pose a significant risk for cancer development.
The doctor selects the removal technique based primarily on the polyp’s size and shape. Small polyps, typically less than 10 millimeters, are often removed using cold snare polypectomy. This technique uses a wire loop to cut the polyp without applying electrical current, minimizing the risk of bleeding and deep tissue injury. For larger sessile polyps, or those that are particularly flat, the doctor may perform an Endoscopic Mucosal Resection (EMR). EMR involves injecting a fluid solution beneath the polyp to lift it away from the deeper muscle layer before the growth is removed.
Understanding Your Results and Surveillance
The final determination of the polyp’s nature rests on the pathology report, which typically becomes available within a few days to a week. The report will detail the polyp’s classification, whether it was benign, a precancerous adenoma, or an actual adenocarcinoma (confirmed cancer). The presence of high-grade dysplasia indicates the cells were highly abnormal and close to becoming invasive cancer.
The results of this pathology report are used to determine the patient’s future surveillance schedule, which is designed to prevent the formation of new cancers. Finding only small, low-risk hyperplastic polyps may mean the next colonoscopy is scheduled in ten years, the standard interval for average-risk individuals. Conversely, the presence of multiple large adenomas, polyps with high-grade dysplasia, or sessile serrated lesions will necessitate a much shorter follow-up time, often in one, three, or five years.
This personalized surveillance strategy is a direct consequence of the pathology findings for effective, long-term colorectal cancer prevention. Adherence to this schedule ensures that any new polyps are detected and removed before they progress to cancer. The doctor will discuss these findings and the recommended follow-up plan during a post-procedure consultation.