Understanding Your Colonoscopy Biopsy Report

by Jason Wasserman MD PhD FRCPC
March 18, 2026

A colonoscopy is the most common procedure for examining the large intestine, which includes the colon and rectum. During a colonoscopy, your doctor may remove tissue samples or entire growths from the lining of the colon and send them to a pathology laboratory for examination. The resulting pathology report describes what was found and can include findings ranging from completely normal tissue to precancerous polyps to cancer. This article explains what a colonoscopy biopsy involves, how the laboratory processes the tissue, and what the terms and findings in your report mean.

What happens during a colonoscopy?

During a colonoscopy, your doctor inserts a thin, flexible instrument called a colonoscope through the rectum and guides it through the entire length of the large intestine. The colonoscope has a camera at the tip that transmits images to a screen, allowing the doctor to examine the lining of the colon in detail.

If an abnormal area is seen — such as a polyp, a raised or flat lesion, or an area of redness or irregular texture — the doctor will either remove it entirely or take a small tissue sample for examination. Tissue removal during colonoscopy can be done in several ways:

Biopsy forceps. A small tool passed through the colonoscope that pinches off a tiny piece of tissue. This is used when the doctor wants to sample an area without removing a large amount of tissue — for example, to evaluate inflammation or to confirm the nature of a flat lesion.
Polypectomy. The removal of a polyp using a wire loop called a snare, which is passed around the base of the polyp and tightened to cut it free. Smaller polyps may be removed with biopsy forceps. This is both a diagnostic and therapeutic procedure — the polyp is removed and sent for examination at the same time.
Endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD). More extensive techniques are used to remove larger or flat lesions that cannot be removed by simple snaring. These techniques allow the pathologist to assess whether the lesion was removed completely.

All tissue removed during a colonoscopy is sent to a pathology laboratory, where a pathologist examines it under a microscope and writes a report.

What does the pathology laboratory do with the tissue?

Once the tissue arrives at the laboratory, it is placed in a preservative solution called formalin. The specimen is first examined with the naked eye — this is called the gross description — and then processed, embedded in paraffin wax, and cut into very thin slices that are placed on glass slides. The slides are stained with special dyes, most commonly hematoxylin and eosin, which highlight different structures within the tissue. The pathologist then examines the slides under the microscope and writes the report.

Additional special stains or immunohistochemistry tests may be ordered if the initial examination raises questions about the nature of the tissue or the type of disease present.

Understanding the layers of the colon wall

Many of the terms in a colonoscopy biopsy report refer to specific layers of the colon wall. Understanding these layers helps clarify how deeply a lesion has grown, which is one of the most important questions the pathology report answers.

Mucosa. The innermost lining of the colon is made up of epithelial cells that form glands called crypts. This is where the colon absorbs water and where most polyps and cancers begin.
Lamina propria. A thin layer of connective tissue immediately beneath the epithelium. It supports the mucosal glands and contains small blood vessels, lymphatic channels, and immune cells.
Muscularis mucosae. A thin layer of muscle at the base of the mucosa. Its presence is an important landmark for pathologists when assessing invasion.
Submucosa. A layer of connective tissue below the muscularis mucosae, containing larger blood vessels and lymphatic channels. When cancer reaches the submucosa, it is classified as T1 disease and is capable of lymphatic spread.
Muscularis propria. The thick muscular layer that contracts to move contents through the colon. Invasion of this layer indicates more advanced disease.
Pericolorectal tissues. The fat and connective tissue surrounding the outer wall of the colon. Cancer extending into this layer is T3 disease.

Normal layers of the colon

What are the most common findings in a colonoscopy biopsy report?

A colonoscopy biopsy report can include a wide range of findings depending on why the colonoscopy was performed and what the doctor observed during the procedure. The following are the findings that patients most commonly encounter.

Normal colonic mucosa

If the tissue looks entirely normal under the microscope, the report will state that the colonic mucosa is within normal limits or that no significant abnormality is identified. This is the most reassuring result.

Hyperplastic polyp

A hyperplastic polyp is the most common type of colon polyp. It is composed of cells that have slightly overgrown but are not considered precancerous. The cells show a sawtooth pattern under the microscope but lack the structural changes that would make them precancerous. Small hyperplastic polyps, particularly in the left colon and rectum, generally do not require any additional follow-up beyond routine surveillance.

Tubular adenoma

A tubular adenoma is the most common type of precancerous colon polyp. It is made up of abnormal gland-forming cells arranged in a tube-like pattern under the microscope. All adenomas are considered precancerous because they have the potential to develop into adenocarcinoma over time if not removed. The degree of cellular abnormality is described as low-grade dysplasia or high-grade dysplasia. Low-grade dysplasia is far more common and carries a lower risk of progression. High-grade dysplasia means the cells are more abnormal and the risk of progression to cancer is higher, warranting closer follow-up.

Tubulovillous adenoma and villous adenoma

A tubulovillous adenoma has a mixture of tube-like and finger-like (villous) growth patterns. A villous adenoma is made up predominantly of finger-like projections. Both are considered more advanced than tubular adenomas and carry a higher risk of progression to cancer. They are also more likely to be classified as advanced adenomas, which require closer surveillance after removal.

Sessile serrated lesion

A sessile serrated lesion (also called a sessile serrated adenoma or SSA/P) is a type of flat polyp that develops through a different biological pathway than conventional adenomas. It shows a distinctive sawtooth pattern in its glandular tissue under the microscope, particularly at the base of the crypts. Although not as high-risk as a conventional adenoma with high-grade dysplasia, sessile serrated lesions are considered precancerous, especially when dysplasia is present or when the lesion is larger than 1 centimetre. They are responsible for a significant proportion of colon cancers, including many cases of mismatch repair-deficient colorectal cancer.

Traditional serrated adenoma

A traditional serrated adenoma is a less common serrated polyp that combines features of conventional adenomas and serrated polyps. It is considered precancerous and is managed similarly to other advanced adenomas.

Adenocarcinoma

If the biopsy shows adenocarcinoma, this means cancer has been identified. Adenocarcinoma is the most common type of colorectal cancer and arises from the gland-forming cells of the colon lining. The pathology report will describe the type, grade, and, when assessable on biopsy, features such as lymphovascular invasion and depth of invasion. A full assessment of the stage is typically performed after surgical resection of the tumour.

Inflammatory findings

Biopsies taken from inflamed areas of the colon may show a range of inflammatory changes. These are commonly seen in conditions such as inflammatory bowel disease.

Chronic active colitis. A pattern of inflammation in which both long-standing (chronic) and active (acute) inflammatory changes are present together. This pattern is seen in inflammatory bowel disease, particularly ulcerative colitis and Crohn’s disease, but can also result from infection or other causes.
Focal active colitis. A pattern in which active inflammation is present in only some of the tissues examined. This is often a non-specific finding that can be caused by infection, medication effects, or early inflammatory bowel disease.
Microscopic colitis. A condition in which the colon appears normal during colonoscopy but shows distinctive changes under the microscope. There are two main subtypes: collagenous colitis, in which there is a thickened band of collagen beneath the surface lining, and lymphocytic colitis, in which there is an excess of lymphocytes within the surface epithelium. Microscopic colitis typically causes chronic, watery diarrhea.

Key terms you may see in your report

Dysplasia

Dysplasia means that the cells look abnormal under the microscope — they have changed in size, shape, or organization in a way that is not yet cancer but indicates a precancerous state. Dysplasia in a colon biopsy is graded as either low-grade or high-grade.

Low-grade dysplasia. The cells show mild to moderate abnormality. The overall structure of the glands is preserved. This is the most common finding in precancerous colon polyps and carries a lower short-term risk of progression to cancer.
High-grade dysplasia. The cells show severe abnormality. The glandular structure is significantly distorted. High-grade dysplasia in a colon polyp indicates a much greater risk of cancer and requires prompt and complete removal, along with closer follow-up surveillance.

Margins

The margin is the edge of the tissue removed during the procedure. The pathologist examines the margin to determine whether the polyp or lesion was completely removed.

Negative margin (clear margin). No abnormal cells are found at the edge of the removed tissue. This suggests the polyp was completely removed.
Positive margin. Abnormal cells are present at the very edge of the removed tissue. This suggests some abnormal tissue may have been left behind and may require a repeat colonoscopy or further treatment.
Cannot be assessed. Some polyps are removed in multiple fragments, or the tissue is cauterized at the edges during removal, making it impossible to assess the margin reliably. Your doctor will advise on appropriate follow-up.

Polypectomy site

A biopsy is sometimes taken from the area of the colon where a polyp was previously removed to check whether it has grown back or if any abnormal tissue remains. The report will describe whether normal colonic tissue, residual polyp, or other abnormalities are present at that site.

Adenoma with carcinoma (malignant polyp)

Occasionally, a polyp that appears benign on colonoscopy is found to contain a focus of carcinoma on microscopic examination. This is called a malignant polyp. Whether further treatment beyond the colonoscopy is needed depends on several pathological features, including how deeply the cancer has invaded, whether the margins are clear, whether lymphovascular invasion is present, and the grade of the cancer. Your doctor will review these features with you to determine the safest next step.

Mismatch repair (MMR) testing

If colon cancer is identified, your pathology report may include results from mismatch repair (MMR) testing. MMR proteins help the cell repair errors that occur during DNA replication. When one or more of these proteins is absent or not functioning correctly, the cancer is described as mismatch repair deficient (dMMR). When all proteins are present and working, the cancer is described as mismatch repair proficient (pMMR).

MMR status is important for two reasons. First, dMMR colorectal cancers may have a better overall prognosis and often respond well to immunotherapy. Second, dMMR can be a sign of Lynch syndrome, an inherited condition that significantly increases the lifetime risk of colorectal cancer and several other cancers. If your report shows dMMR, your doctor will discuss whether further genetic testing is appropriate for you and your family members.

The MMR status is assessed by immunohistochemistry, which uses special stains to check whether four proteins — MLH1, MSH2, MSH6, and PMS2 — are present in the cancer cells. A loss of staining for any of these proteins indicates dMMR. If MLH1 staining is lost, an additional test, MLH1 promoter methylation testing, is often performed to determine whether the loss is due to Lynch syndrome or a sporadic (non-inherited) cause.

What happens after the colonoscopy biopsy report?

Once your doctor has reviewed the pathology report, they will discuss the findings with you and explain what they mean for your follow-up plan. The recommendations that follow depend on what was found.

If only normal tissue or hyperplastic polyps were found

If no precancerous or cancerous findings were identified, your doctor will advise on when your next colonoscopy should be, based on your age, personal history, and family history of colon cancer. For most people with a normal colonoscopy and no significant risk factors, the next screening colonoscopy is recommended in ten years.

If one or more adenomas were found and removed

The timing of your next colonoscopy will depend on the number, size, type, and grade of the adenomas found. Current guidelines generally recommend a surveillance colonoscopy in three to five years for most adenomas. Larger or more advanced adenomas may prompt earlier follow-up. Your doctor will advise you on the appropriate interval based on your specific findings.

If sessile serrated lesions were found

Sessile serrated lesions without dysplasia are typically followed by colonoscopy in three to five years, similar to conventional adenomas. Those with dysplasia or those who are large may prompt earlier follow-up.

If inflammatory bowel disease is suspected or confirmed

If the biopsy findings suggest inflammatory bowel disease, such as ulcerative colitis or Crohn’s disease, your doctor may refer you to a gastroenterologist for further evaluation and management. People with long-standing inflammatory bowel disease require regular colonoscopic surveillance because the chronic inflammation increases the long-term risk of colorectal cancer.

If cancer were found

If adenocarcinoma was identified in the biopsy, your doctor will arrange further imaging studies to assess the extent of the disease and refer you to a surgeon or oncologist to discuss treatment options. Surgery is the primary treatment for most colorectal cancers and may be combined with chemotherapy and radiation, depending on the stage and location of the cancer.

Questions to ask your doctor

What was found in my colonoscopy biopsy?
If a polyp was found, what type is it, and is it precancerous?
Was the polyp or lesion completely removed?
Was dysplasia found, and if so, is it low-grade or high-grade?
Do I need any additional procedures or treatment?
When should I have my next colonoscopy?
If cancer were found, what is the next step?
Was mismatch repair testing done, and what were the results?
Based on my findings, should my family members or I be referred for genetic counselling?
Are there any lifestyle changes I can make to reduce the risk of new polyps or cancer?