What Does a Positive or Indeterminate Adenoma Margin Mean?

Seeing the words “positive margin” or “cannot be assessed” on your colon pathology report can be terrifying. However, when dealing with a colon adenoma, these phrases usually describe technical uncertainty about the edge of the specimen rather than a diagnosis of cancer.

If your report confirms the polyp is an adenoma with no invasive cancer, an involved or indeterminate margin simply means the pathologist cannot guarantee the entire adenoma was removed. It means there is a chance some adenoma cells remain at the resection site—it does not mean you have invasive cancer left behind ^[1][2].

Understanding Key Pathology Terms

To better understand your report, it helps to know a few key terms:

• Adenoma: A precancerous type of polyp.
• Dysplasia: Abnormal cells within the polyp. Most adenomas have low-grade dysplasia, but some have high-grade dysplasia (more advanced, but still not invasive cancer).
• Invasive Carcinoma: Cancer cells that have grown beyond the surface lining and deeper into the colon wall ^[3].
• Margin: The cut edge of the removed tissue ^[1]. There are lateral (side) margins and deep/vertical (bottom) margins.

What the Margin Results Mean

When a polyp is removed, the pathologist looks at the margins under a microscope to see if adenoma cells go all the way to the cut line.

• Negative (Clear) Margin: No adenoma is seen at the examined cut edges. While reassuring, it does not perfectly guarantee that absolutely no tissue was left behind, especially if the polyp was large or removed in pieces ^[4].
• Positive (Involved) Margin: Adenoma cells touch the examined cut edge. This suggests a small amount of the precancerous polyp may still be in the colon ^[1].
• Indeterminate (Cannot be Assessed): The pathologist cannot clearly evaluate the edges to make a definitive judgment ^[5].

Why Are Margins Sometimes Unassessable?

It is very common for margins to be reported as indeterminate, especially for larger polyps. This happens for several technical reasons:

• Piecemeal Removal: Large polyps are often removed in multiple pieces (piecemeal resection) rather than in one single chunk (en bloc removal). When the tissue is in pieces, the pathologist usually cannot reconstruct the exact outer edge to check for completeness ^[5].
• Fragmentation: Even if removed in one piece, delicate polyp tissue can break apart during removal or transport to the lab, making the margin indefinable ^[5].
• Cautery Artifact: Doctors often use instruments with heat (electrocautery) to remove polyps and stop bleeding. This heat can distort or obscure the cut edge of the tissue, preventing a clear assessment under the microscope.

What Happens Next?

A positive or indeterminate margin on a non-invasive adenoma is not a medical emergency ^[1]. (Note: Always seek urgent medical care if you experience heavy rectal bleeding, severe abdominal pain, or fever after a colonoscopy).

Because the main risk is simply that some precancerous tissue was left behind, the standard approach involves close follow-up with your endoscopist:

• Targeted Follow-Up: Your doctor will likely recommend a follow-up colonoscopy to inspect the scar where the polyp was removed. For large polyps (e.g., 20 mm or larger) removed in pieces, guidelines often recommend checking the scar in about 6 months ^[6]. For smaller polyps, or those removed in one piece, the timing is individualized based on the lesion’s size, your doctor’s visual assessment, and clinical guidelines ^[7].
• Endoscopic Retreatment: If there is visible residual adenoma at the scar, it can often be treated endoscopically by an experienced doctor ^[8][9]. The doctor may remove or thermally ablate (burn) the remaining tissue. Because repeat treatment can sometimes be difficult or carry standard procedure risks, you may occasionally be referred to an advanced endoscopist for this step ^[8].
• When is Surgery Considered? Surgery is rarely needed for a simple adenoma. It is generally considered if the pathology report identifies actual invasive cancer with high-risk features (such as a positive deep margin, cancer invading deep into the submucosa, poor cell differentiation, or lymphovascular invasion) ^[10][11]. Surgery might also be discussed if a benign polyp is in a difficult location and simply cannot be safely or completely cleared with colonoscopy techniques ^[12].