A polyp is an abnormal growth of tissue that projects from a mucous membrane. While most are harmless, finding one that is malignant signals an early form of cancer. This diagnosis means the abnormal cells have invaded the layer beneath the inner lining, known as the submucosa. This transitions the polyp from a precancerous lesion into an early-stage carcinoma. The discovery of cancer within a polyp, often after a colonoscopy, initiates a precise medical process designed to determine the extent of the disease and establish a definitive treatment strategy.
Pathology, Grading, and Staging
The immediate step following the discovery of cancer within a polyp is a thorough analysis by a pathologist. This pathology report confirms the diagnosis and provides essential details regarding the tumor’s characteristics and physical depth of invasion. The report assesses the tumor’s grade, which describes how abnormal the cancer cells look compared to healthy cells, with poor differentiation suggesting a more aggressive tumor.
The report also uses specialized classification systems to determine the precise depth of invasion into the submucosa, which is the most significant factor in early-stage polyp cancer. For polyps attached by a stalk (pedunculated), the Haggitt classification defines the level of invasion within the stalk. For flatter polyps (sessile), the Kikuchi or Sm classification measures the invasion by dividing the submucosa into thirds. Deeper invasion into the lower third (Sm3) indicates a higher risk of spread to nearby lymph nodes.
To complete the full staging process, which determines the overall extent of the disease, additional imaging tests are often required. A computed tomography (CT) scan is performed to look for signs of distant spread to organs like the liver or lungs. For polyps located in the rectum, an MRI scan or an endoscopic ultrasound (EUS) is used to assess the rectal wall and local lymph node involvement. This comprehensive diagnostic phase determines the cancer’s location and aggressiveness, which directly informs the subsequent treatment plan.
Choosing the Right Treatment Plan
The treatment selected for a cancerous polyp is highly individualized and depends on the tumor’s stage and the specific high-risk features identified in the pathology report. For a polyp that was fully removed during the initial colonoscopy and shows low-risk features, the endoscopic removal may be considered a complete cure. Low-risk factors include a well- or moderately differentiated tumor, no invasion of blood or lymph vessels (lymphovascular invasion), and a shallow invasion depth (e.g., Sm1).
If the pathology reveals high-risk features, such as a positive or narrow margin of removed tissue, poor differentiation, or deep submucosal invasion (Sm3), the risk of residual cancer or spread to lymph nodes is significant. In these cases, a more extensive surgical procedure is recommended. This operation, known as a formal oncologic resection or colectomy, removes the segment of the colon or rectum containing the original polyp site, along with the adjacent lymph nodes.
For polyps that are large or difficult to access, advanced endoscopic techniques like Endoscopic Mucosal Resection (EMR) or Endoscopic Submucosal Dissection (ESD) are employed to achieve a complete, single-piece removal. These specialized procedures allow for a more accurate assessment of the margins and invasion depth. The decision to proceed with major surgery versus surveillance involves balancing the risk of recurrence against the risks associated with a major operation.
If the cancer has spread beyond the immediate site or is associated with high-risk features, systemic treatments may be added to the plan. Chemotherapy uses drugs to destroy cancer cells throughout the body, while targeted therapy focuses on specific molecular features of the tumor. Treatment decisions are determined through a multidisciplinary approach, where surgeons, oncologists, and radiation specialists collaborate to create the most effective strategy for the patient.
Life After Treatment: Monitoring for Recurrence
Once the primary treatment is complete, the focus shifts to long-term surveillance to monitor for cancer recurrence or the development of new polyps. This follow-up care is important because individuals who have had a cancerous polyp are at a higher risk of developing another one in the future. The surveillance schedule is tailored to the initial risk level, factoring in the stage of the original cancer and the type of treatment received.
The primary tool for long-term monitoring is the follow-up colonoscopy, which allows a physician to visually inspect the site where the polyp was removed and the rest of the colon. For those who had a cancerous polyp removed endoscopically with high-risk features, the first follow-up colonoscopy may be scheduled three to six months after the procedure. For lower-risk cases, the interval is longer, but remains more frequent than for the general population.
Blood tests are often used to monitor for disease recurrence. The Carcinoembryonic Antigen (CEA) test measures a protein that can be elevated when colorectal cancer is present or returns. A rising CEA level serves as an early warning sign, prompting further investigation with imaging scans.