Adenocarcinoma can sometimes develop within a colon or rectal polyp. A polyp is a growth that projects from the inner lining of the colon or rectum. Most polyps are benign (non-cancerous), but some types have the potential to develop into cancer over time. When a cancer starts in a polyp and invades deeper layers of tissue, it is called invasive adenocarcinoma. A pathologist typically makes this diagnosis after examining a tissue sample removed during a colonoscopy or surgery.
Several types of polyps can give rise to adenocarcinoma:
These polyps are considered precancerous because they contain abnormal cells that may become cancerous if not removed. The risk of cancer is higher in larger polyps and in those with certain microscopic features, such as high-grade dysplasia.
When cancer is found in a polyp, the outcome is often more favorable than when it is found in a larger tumor. If the cancer is confined to the polyp and has been completely removed, additional treatment such as surgery may not be necessary. However, certain features in the pathology report help doctors determine whether further treatment is needed to reduce the risk of cancer recurrence or spread.
If the cancer cells in the polyp invade beyond the inner surface (epithelium) and reach the submucosa, it is called invasive adenocarcinoma. Pathologists evaluate how deeply the cancer has invaded using special systems based on the type of polyp.
Haggitt levels are used for pedunculated polyps, which have a stalk like a mushroom:
The deeper the invasion, the higher the risk that cancer may spread to the lymph nodes.
Kikuchi levels are used for sessile polyps, which are flat and do not have a stalk:
Deeper invasion, especially Sm3, is linked to a greater risk of cancer spreading beyond the colon.
If the cancer is confined to the polyp, is well-differentiated, and has not deeply invaded or exhibited other high-risk features, complete removal of the polyp may be deemed curative.
However, surgery to remove a portion of the colon may be recommended if:
These features increase the risk that cancer could spread to lymph nodes, and surgery allows doctors to remove and examine nearby lymph nodes to check for metastasis.
The prognosis is generally excellent when the cancer is completely removed and no high-risk features are present. In many cases, no further treatment is needed. However, if high-risk features are present or if lymph nodes are involved, additional treatment such as surgery or chemotherapy may be recommended.
Understanding your pathology report can help you and your healthcare team make informed decisions about your care.