The large intestine is the final part of the digestive tract. It includes the colon and the rectum, and its main job is to absorb water and to form and store stool. When tissue is removed from the colon or rectum — often during a colonoscopy — a pathologist examines it under a microscope and describes what they see in your pathology report.
This page brings together our guides to conditions found in the colon and rectum. The articles are grouped by type to help you find the one that matches your diagnosis. Some conditions are cancerous, some are precancerous (not cancer, but a change that can increase the risk of cancer over time), and many are not cancer at all. Select any article below to learn more.
Cancers of the colon and rectum
These diagnoses are tumors of the colon and rectum that are cancerous or have the potential to behave like cancer. The most common type is adenocarcinoma. The articles explain how each type is diagnosed and what the details in your pathology report mean.
Adenocarcinoma is the most common type of cancer in the colon and rectum. It develops from the gland-forming cells of the lining. This article explains how it is diagnosed and what the details in your pathology report mean.
You may find this helpful if your report says adenocarcinoma of the colon or rectum, or colorectal cancer.
Mucinous adenocarcinoma is a type of colorectal cancer in which the cancer cells produce a large amount of mucus. This article explains what this diagnosis means and what your report describes.
You may find this helpful if your report mentions mucinous adenocarcinoma of the colon or rectum.
Medullary carcinoma is an uncommon type of colorectal cancer. It is often linked to a change in the cell’s DNA repair system. This article explains what this diagnosis means.
You may find this helpful if your report mentions medullary carcinoma of the colon, or testing for mismatch repair (MMR).
Well differentiated neuroendocrine tumor
A well differentiated neuroendocrine tumor is a slow-growing tumor that develops from hormone-producing cells in the colon or rectum. This article explains how it is diagnosed and what your pathology report describes.
You may find this helpful if your report mentions a well differentiated neuroendocrine tumor or a carcinoid tumor of the colon or rectum.
Poorly differentiated neuroendocrine carcinoma
Poorly differentiated neuroendocrine carcinoma is a fast-growing cancer that develops from hormone-producing cells in the colon or rectum. This article explains how it is diagnosed and what your report describes.
You may find this helpful if your report mentions a poorly differentiated neuroendocrine carcinoma of the colon or rectum.
Precancerous polyps
A polyp is a growth that rises above the surrounding lining. The polyps described here are precancerous: they are not cancer, but they can slowly change into cancer over time, so they are usually removed during a colonoscopy. The articles explain what each diagnosis means.
A tubular adenoma is the most common type of precancerous polyp in the colon. This article explains what this diagnosis means and why these polyps are removed.
You may find this helpful if your report mentions a tubular adenoma after a colonoscopy.
A tubulovillous adenoma is a precancerous polyp of the colon that has a mix of two growth patterns. This article explains what this diagnosis means.
You may find this helpful if your report mentions a tubulovillous adenoma.
A villous adenoma is a precancerous polyp of the colon with a finger-like growth pattern. This article explains what this diagnosis means and why these polyps are removed.
You may find this helpful if your report mentions a villous adenoma.
A sessile serrated lesion is a type of precancerous polyp with a flat shape and a saw-toothed appearance under the microscope. This article explains what this diagnosis means.
You may find this helpful if your report mentions a sessile serrated lesion, also called a sessile serrated adenoma or polyp.
A traditional serrated adenoma is an uncommon type of precancerous serrated polyp of the colon. This article explains what this diagnosis means.
You may find this helpful if your report mentions a traditional serrated adenoma or TSA.
Noncancerous polyps
The polyps described here are not cancer and do not usually develop into cancer. They are often found by chance during a colonoscopy. The articles explain what each diagnosis means.
A hyperplastic polyp is a common, noncancerous polyp of the colon. Most do not carry a risk of becoming cancer. This article explains what this diagnosis means.
You may find this helpful if your report mentions a hyperplastic polyp after a colonoscopy.
An inflammatory polyp is a noncancerous growth in the colon that forms as a reaction to inflammation or injury. This article explains what this diagnosis means.
You may find this helpful if your report mentions an inflammatory polyp of the colon or rectum.
Inflammatory and other conditions
These diagnoses describe inflammation and other noncancerous conditions of the colon and rectum. The articles explain what each diagnosis means and what a pathologist looks for.
Chronic active colitis means the lining of the colon shows both long-lasting and ongoing inflammation. This article explains what this diagnosis means and what may cause it.
You may find this helpful if your report mentions chronic active colitis, which can be a sign of inflammatory bowel disease.
Focal active colitis means there are small, scattered areas of ongoing inflammation in the lining of the colon. This article explains what this diagnosis means.
You may find this helpful if your report mentions focal active colitis.
Microscopic colitis is inflammation of the colon that can only be seen under the microscope. It is a common cause of ongoing watery diarrhea. This article gives an overview of the diagnosis and its two main types.
You may find this helpful if your report mentions microscopic colitis, or you have ongoing watery diarrhea.
Collagenous colitis is a type of microscopic colitis defined by a thickened band of collagen under the lining of the colon. This article explains what this diagnosis means.
You may find this helpful if your report mentions collagenous colitis.
Lymphocytic colitis is a type of microscopic colitis defined by an increased number of immune cells in the lining of the colon. This article explains what this diagnosis means.
You may find this helpful if your report mentions lymphocytic colitis.
Diverticular disease is a common condition in which small pouches form in the wall of the colon. It is not cancer. This article explains what this diagnosis means and what a pathologist looks for.
You may find this helpful if your report mentions diverticular disease, diverticulosis, or diverticulitis.
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