Your pathology report for adenocarcinoma in a colorectal polyp

by Jason Wasserman MD PhD FRCPC
May 21, 2025

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.

What types of polyps can develop cancer?

Several types of polyps can give rise to adenocarcinoma:

  • Tubular adenoma
  • Tubulovillous adenoma
  • Villous adenoma
  • Sessile serrated lesion

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.

Why is adenocarcinoma in a polyp important to identify?

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.

How do pathologists assess invasion in a polyp?

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

Haggitt levels are used for pedunculated polyps, which have a stalk like a mushroom:

  • Level 1: Cancer is limited to the head of the polyp.
  • Level 2: Cancer has spread into the neck of the polyp.
  • Level 3: Cancer has invaded the stalk.
  • Level 4: Cancer has spread beyond the stalk into the submucosa of the colon wall.

The deeper the invasion, the higher the risk that cancer may spread to the lymph nodes.

Kikuchi levels

Kikuchi levels are used for sessile polyps, which are flat and do not have a stalk:

  • Sm1: Superficial submucosal invasion.
  • Sm2: Intermediate invasion into the submucosa.
  • Sm3: Deep submucosal invasion.

Deeper invasion, especially Sm3, is linked to a greater risk of cancer spreading beyond the colon.

When is surgery recommended?

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:

  • The margins are not clear (cancer cells are close to the edge of the removed tissue).
  • The cancer is poorly differentiated (high grade).
  • There is lymphovascular invasion (cancer seen in small blood vessels or lymphatic vessels).
  • There is perineural invasion (cancer growing around nerves).
  • The depth of invasion is at Haggitt level 4 or Sm3.
  • Tumor budding (small clusters of cancer cells at the invasive edge) is high.

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.

What is the prognosis for adenocarcinoma in a polyp?

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.

Questions for your doctor

  • Was the cancer completely removed?
  • What type of polyp did the cancer arise in?
  • How deep did the cancer invade?
  • Are the margins clear?
  • Was there any lymphovascular or perineural invasion?
  • Do I need surgery or further treatment?
  • Will any additional testing be done to check for cancer spread?

Understanding your pathology report can help you and your healthcare team make informed decisions about your care.

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