Colorectal Cancer: Diagnosis & Staging

Pictured: Robin Mendelsohn Gastroenterologist Robin Mendelsohn (center) starts a procedure in one of our state-of-the-art endoscopy suites. Getting an accurate diagnosis is essential for optimizing treatment.

Increased screening for colorectal cancer has led to an increase in the detection of the disease. Treatment for all cases of colorectal cancer is not the same, however. Getting an accurate diagnosis is essential for determining the best treatment approach for each individual patient.

Because physicians at Memorial Sloan Kettering subspecialize in diagnosing and treating only colorectal cancer, we bring a high degree of expertise to understanding your disease. Our board-certified physicians will work as a multidisciplinary team to review your case. The team includes pathologists who specialize in colorectal cancer.

In addition to performing standard diagnostic tests, Memorial Sloan Kettering is helping to lead the field of personalized medicine for colorectal cancer, looking at specific genes in tumor cells that can help determine the best course of treatment. 

Diagnostic Tests

Colorectal cancer screening and diagnosis may involve one or more of the following procedures:

Colonoscopy: A colonoscopy is the most effective way to detect polyps in the colon and rectum. Before the procedure, patients must follow a special clear-liquid diet and take a medicine to clear the bowel. During the colonoscopy, you will receive a mild sedative, and the doctor will insert a tube with a light, a camera, and other tools on its tip into the rectum and colon. As the camera transmits images to a screen, your doctor looks for polyps. If there are polyps, the doctor can usually remove them immediately and send them to a pathologist for examination.

Flexible Sigmoidoscopy: This examination is similar to the colonoscopy exam, but it uses a shorter tube to inspect the lower part of the colon.

Virtual Colonoscopy: In a virtual colonoscopy, CT scans are taken to create a 3-D image of the bowel. While this technique is an effective option for some people who can't or don't want to undergo a colonoscopy, the doctor is not able to perform a biopsy or remove a polyp if an abnormality is found. A virtual colonoscopy requires the same bowel-cleansing procedure as conventional colonoscopy.

Fecal Occult Blood Test: Because bleeding in the colon or rectum can be a sign of colorectal cancer, the fecal occult blood test may be used to check for blood in the stool. On three successive days, you will be asked to place small stool samples on special, chemically treated cards and then send them to a doctor or laboratory for testing. Your doctor will ask you to follow a special diet to ensure accurate results.

Fecal Immunochemical Test (FIT) : Also called an immunochemical fecal occult blood test (iFOBT), this newer type of colorectal cancer screening test also detects blood in the stool, but it does so by reacting to a part of the hemoglobin molecule (a protein found in red blood cells). Unlike traditional fecal occult blood testing, FIT does not require you to avoid certain foods or drugs before the test.

Personalized Medicine for Colorectal Cancer

Colorectal cancer can involve a variety of genetic mutations that cause normal cells to become cancerous. These genetic changes (called somatic mutations) are found only in cancer cells, not in your normal cells. They cannot be passed on to your children.


Our physicians consider the extent of a tumor and its genetic characteristics when planning treatment.


During the process of identifying your diagnosis, Memorial Sloan Kettering’s pathologists will conduct molecular testing on the tumor to determine whether specific mutations are present. This, in turn, can indicate certain aspects of how the tumor will behave and how it will react to certain treatments. Knowing as much as possible about the genetic makeup of the tumor helps to ensure that you get the treatments most likely to help you and to avoid drugs (and accompanying side effects) that will not benefit you.

In 2010, Memorial Sloan Kettering began using a new technology to conduct routine genetic analyses of biopsy samples from patients with colorectal cancer. The innovative method tests for mutations in the genes EGFR, KRAS, and BRAF, which are common in colorectal cancer, as well as mutations in other less well-known genes. This advanced technology can provide results more quickly and be used to look for multiple mutations at the same time. It is also more sensitive, allowing our pathologists to perform molecular testing on biopsy samples that contain fewer tumor cells than were required using previous approaches.

Memorial Sloan Kettering is the only hospital in the New York metropolitan area using such technology to practice this kind of real-time, personalized medicine. As more colorectal tumors are sampled and tested, our researchers will be able to investigate mutations in lesser-known genes and enroll patients in clinical trials for new, experimental, targeted drugs.

If your testing indicates that the tumor has certain genetic characteristics, you may also be eligible to participate in a clinical trial.


If tests show that you have colorectal cancer, additional examinations will be performed to determine how far it has spread through the body — a process called staging. Knowing how far your cancer has progressed enables your doctor to plan the treatment strategy that is best for you.

The following tests are routinely used to stage colorectal cancer:

  • CT (computed tomography) and MRI (magnetic resonance imaging) scans, which may be used to see if the cancer has spread to other organs, such as the liver and lungs
  • Chest x-ray, which can also show if the cancer has spread to the lungs
  • Blood tests for CEA, a protein that acts as a marker for colorectal cancer

Depending on your specific clinical situation, these additional tests may be ordered:

  • PET (positron emission tomography) scanning. PET scans can show if the cancer has spread to other parts of the body.
  • Angiography, which can locate blood vessels next to a cancer that has spread to the liver. Knowing where these blood vessels are enables doctors to minimize blood loss during surgery.
  • Endorectal ultrasound probe, which uses sound waves to produce an image of the tumor. The probe is placed in the rectum to see how far a cancer has invaded the rectal wall. This procedure is used for staging rectal cancer only.