Most colorectal cancer is found through a colonoscopy. A colonoscopy is a procedure done under sedation. The physician places a thin, tube-like instrument with a light and a lens for viewing inside the rectum and colon. The scope may also have a tool to remove polyps or tissue samples which are checked for cancer in a lab.
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Penn Medicine answered
A colonoscopy can usually determine if a patient has colon cancer. In this video, Daniel Labow, MD, an oncology surgeon at The Mount Sinai Medical Center, describes the symptoms that might show up before a colonoscopy is performed.
Lisa Ganjhu, DO, Gastroenterology, answered
Screening is the number-one way colon cancer is diagnosed, but it’s not the only way, according to gastroenterologist Dr. Lisa Ganjhu. Watch the video to learn which early symptoms of colon cancer to watch for.
Barium enema: This diagnostic test allows the doctor to evaluate the entire large intestine with an X-ray. Barium, a contrast dye, is placed into the bowel using an enema, and air may also be added. The barium fills and coats the lining of the bowel, creating a clear outline of the rectum, colon, and occasionally a small portion of the small intestine. A flexible sigmoidoscopy is often done in addition to the barium enema to aid in detecting small polyps that a barium enema X-ray may miss. This commonly occurs in the lower bowel and rectum.
Colonoscopy: This procedure is the most sensitive test for colon cancer, rectal cancer, and polyps. Colonoscopies are similar to flexible sigmoidoscopies, but the instrument used is a colonoscope, a long, flexible, and slender tube attached to a video camera and monitor. This allows the doctor to view the entire colon and rectum. If any polyps are found during the exam, the doctor may remove them immediately or take tissue samples (biopsies) for analysis. This is done through the colonoscope and is virtually painless, but the patient may receive a mild sedative for comfort. Preparation for the procedure involves drinking a large amount of fluid containing a laxative to clean out the colon.
Blood tests: Blood tests may include a test for anemia (if bleeding occurs). A newer test checks a stool sample for DNA of abnormal cells. It is called the carcinoembryonic antigen (CEA) assay. It is useful because CEA is released into the bloodstream from both cancer cells and normal cells, and has been found in colon cancer.
Biopsy: For a biopsy, the doctor removes a small piece of tissue that is sent to the lab and examined under the microscope to see if any cancer is present.
PET scan (positron emission tomography): PET scans for colon cancer use a type of radioactive sugar, because cancer cells absorb high amounts of sugar. A special camera is used to visualize where the cancerous cells may reside.
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Riverside Cancer Care Center answered
The following tests and procedures may be used:Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient's health habits and past illnesses and treatments will also be taken. Fecal occult blood test: A test to check stool (solid waste) for blood that can only be seen with a microscope. Small samples of stool are placed on special cards and returned to the doctor or laboratory for testing. Digital rectal exam: An exam of the rectum. The doctor or nurse inserts a lubricated, gloved finger into the rectum to feel for lumps or anything else that seems unusual. Barium enema: A series of x-rays of the lower gastrointestinal tract. A liquid that contains barium (a silver-white metallic compound) is put into the rectum. The barium coats the lower gastrointestinal tract and x-rays are taken. This procedure is also called a lower GI series. Sigmoidoscopy: A procedure to look inside the rectum and sigmoid (lower) colon for polyps (small pieces of bulging tissue), abnormal areas, or cancer. A sigmoidoscope is inserted through the rectum into the sigmoid colon. A sigmoidoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove polyps or tissue samples, which are checked under a microscope for signs of cancer. Colonoscopy: A procedure to look inside the rectum and colon for polyps, abnormal areas, or cancer. A colonoscope is inserted through the rectum into the colon. A colonoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove polyps or tissue samples, which are checked under a microscope for signs of cancer. Biopsy: The removal of cells or tissues so they can be viewed under a microscope by a pathologist to check for signs of cancer. Virtual colonoscopy: A procedure that uses a series of x-rays called computed tomography to make a series of pictures of the colon. A computer puts the pictures together to create detailed images that may show polyps and anything else that seems unusual on the inside surface of the colon. This test is also called colonography or CT colonography.
This answer is based on source information from the National Cancer Institute.