A cancerous polyp, or malignant polyp, is a colorectal adenoma that has transformed into an adenocarcinoma and begun to invade the deeper layers of the bowel wall. This diagnosis occurs when cancer cells grow through the muscularis mucosae and into the underlying submucosa of the polyp. While most polyps found during routine colonoscopies are benign or pre-cancerous, this early invasion classifies the lesion as true colorectal cancer. Because the cancer is typically caught at this earliest stage (T1), the chance for a complete cure remains very high. The need for further intervention depends entirely on a detailed analysis of the removed tissue.
Confirming the Diagnosis and Staging the Cancer
The immediate step following discovery is a comprehensive pathology review, which examines the excised polyp under a microscope to confirm the depth and nature of the invasion. Pathologists look for specific adverse features that indicate a higher risk of the cancer having spread beyond the polyp. A primary factor is the depth of submucosal invasion, measured by the distance the cancer has penetrated from the muscularis mucosae.
In sessile (flat or broad-based) polyps, the submucosal layer is divided into sm1, sm2, and sm3. Invasion into the deeper sm3 layer indicates an increased risk of lymph node involvement. For all polyps, an invasion depth greater than 1,000 micrometers is a high-risk feature suggesting the need for more aggressive treatment. Pathologists also determine the cancer’s grade, noting whether cells are well-differentiated (low-grade) or poorly-differentiated (high-grade).
The specimen is also checked for lymphovascular invasion, where cancer cells are visible within the blood vessels or lymphatic channels inside the polyp. The presence of poorly differentiated cells or lymphovascular invasion predicts that the cancer may have traveled to nearby lymph nodes. Finally, the pathologist assesses the margin, the surrounding healthy tissue removed with the polyp. If cancer cells are found less than one millimeter from the cut edge, the margin is considered positive. These high-risk features are used to stage the cancer (Stage T1) and guide the decision for additional treatment beyond the initial polypectomy.
Treatment Options Based on Cancer Progression
The treatment pathway after a malignant polyp diagnosis depends on whether the pathology report identifies any adverse, high-risk features. For a low-risk malignant polyp—defined as a well-differentiated tumor with shallow submucosal invasion, clear margins, and no lymphovascular invasion—the initial endoscopic removal is often considered curative. In these circumstances, the colonoscopy procedure successfully removes all cancerous tissue, and no further surgery or systemic therapy is required.
If the pathology report indicates one or more high-risk features, a more extensive treatment is necessary due to the increased chance of residual cancer cells or lymph node spread. This usually involves a surgical resection, known as a partial colectomy. During this procedure, a segment of the colon containing the original polyp site and surrounding lymph nodes is removed. This surgery clears any cancer that may have spread to the local lymph nodes, an occult risk that cannot be ruled out otherwise. Studies show that 10 to 15 percent of patients with high-risk T1 lesions who undergo surgery have residual cancer or positive lymph nodes in the surgical specimen.
Systemic therapy, such as chemotherapy, is generally not applicable for a low-risk T1 lesion that has been completely removed. However, if the partial colectomy reveals cancer spread to local lymph nodes, the diagnosis is upgraded to Stage III. Adjuvant chemotherapy is then recommended to eliminate microscopic cancer cells that may have spread elsewhere. Chemotherapy or radiation therapy is primarily reserved for patients whose cancer is more advanced or whose surgical pathology confirms involvement beyond the bowel wall or lymph node spread.
Long-Term Monitoring and Survivorship
Following successful treatment, patients enter a phase of rigorous long-term monitoring, or surveillance, to watch for cancer recurrence or the development of new polyps. The follow-up schedule is accelerated compared to standard screening guidelines to ensure the earliest possible detection of issues. Patients who had a high-risk polyp removed or underwent a partial colectomy typically have their first follow-up colonoscopy one year after the procedure.
The frequency of subsequent colonoscopies is determined by the findings of the first surveillance exam, often continuing at one to three-year intervals for several years. Blood tests are also integrated into the monitoring plan, most notably the Carcinoembryonic Antigen (CEA) test. CEA is a tumor marker that can be elevated in the presence of colorectal cancer. Regular testing, typically every three to six months for the first two to three years, helps track the response to treatment and can be an early indicator of recurrence.
Survivorship care also focuses on lifestyle adjustments to reduce the risk of future polyp formation and cancer recurrence. Patients are encouraged to maintain a healthy weight, incorporate regular physical activity, and adopt a diet rich in fiber, fruits, and vegetables. This comprehensive approach, combining medical surveillance with proactive health choices, fosters a healthy transition back to routine life following the diagnosis and treatment.