Rectal cancer is often found after symptoms appear. But most people with early-stage rectal cancer don’t have symptoms. Those usually only develop with more-advanced disease. That’s why we recommend regular screening tests to detect the disease at an early stage, when it’s easier to treat.

If you have symptoms that suggest you may have rectal cancer, your doctor will take your medical history, perform a physical examination, and likely order diagnostic tests.

Colonoscopy and Biopsy for Rectal Cancer Diagnosis 

If we suspect that you may have rectal cancer based on those results, one of our specialists will do a colonoscopy and take a biopsy. In this test, a doctor removes a small piece of tissue with a special instrument. One of our expert pathologists (doctors who specialize in diagnosing disease) then examines the tissue sample under a microscope.

Your care team may recommend CT and MRI scans to determine the stage of the cancer and to see if it has spread to other organs. 

Genetic Testing for Rectal Cancer

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

For some advanced cancers, pathologists at Memorial Sloan Kettering will do molecular testing on the tumor to find somatic mutations. These mutations can predict how a tumor might react to treatments. Knowing as much as possible about a tumor’s genetic makeup can help your care team choose the treatments that are most likely to help you.

If the cancer has spread outside the rectum, your doctor will test tumor samples for mutations in genes called EGFR, KRAS, and BRAF. These are common in rectal cancer. We will also test for mutations in less common genes.