Colorectal Cancer Diagnosis

Colorectal cancer is often found after symptoms appear, but most people with early colon or rectal cancer don’t have symptoms, which usually only develop with more advanced disease. This is why we recommend regular screening tests to detect the disease at an early stage when it’s easier to treat.

If your doctor finds something suspicious during a screening exam, or if you have any of the symptoms of colorectal cancer, he or she will take your medical history to check for symptoms and risk factors and will probably recommend exams and tests to find the cause. These tests may include a physical exam, such as feeling your abdomen; certain blood tests; and a colonoscopy.

If we suspect you may have colorectal cancer based on your initial exam and tests, our specialists will take a biopsy sample during a colonoscopy. In a biopsy, the doctor removes a small piece of tissue with a special instrument inserted through the rectum. One of the expert pathologists (doctors who specialize in diagnosing disease) at Memorial Sloan Kettering then examines the tissue sample under a microscope.


If your treatment team diagnoses you with colorectal cancer, the next critical step is figuring out the stage of the cancer, or how advanced it is. Staging helps us design a treatment plan that attacks your cancer in the most effective way possible. To determine the stage of your cancer, your team runs tests to figure out two things:

  • how deep the cancer has spread through your colon
  • whether the cancer has metastasized (spread) to other parts of your body

Your treatment team may recommend the following tests:

  • CT and MRI scans to show if the cancer has metastasized to other organs
  • CEA blood tests to detect CEA, a protein that’s a marker for colorectal cancer

Genomic Testing

Colorectal cancers can involve a number of different genetic mutations that cause normal cells to become cancerous. These changes in the genes, called somatic mutations, are found only in cancer cells. They are not found in your normal cells and they can’t be passed down to your children.

For stage 4 cancers, pathologists at Memorial Sloan Kettering will do molecular testing on the tumor to detect somatic mutations. These mutations can indicate certain behaviors of the tumor and predict how it might react to certain treatments. Knowing as much as possible about the tumor’s genetic makeup can help your treatment team choose a plan of care that’s most likely to help you.

If you have metastatic diseases, your doctor will test biopsy samples for mutations in genes called EGFR, KRAS, and BRAF, which are common in colorectal cancer, as well as mutations in other less common genes. This advanced tool can look for multiple mutations at once and provide quicker results. It’s also more sensitive, allowing our pathologists to test biopsy samples that have fewer tumor cells.