Colon and rectal cancers are most often found during a routine screening colonoscopy or when symptoms are present and a colonoscopy is necessary to find the cause. If possible, your doctor will remove any areas of concern during a screening colonoscopy and have them tested in a lab to see if cancer is present. If the biopsy results show that pre-cancerous cells or cancer cells are present, additional testing and procedures are needed.
- A diagnostic colonoscopy is nearly the same as a screening colonoscopy. However, this time, the doctor is looking to see if there are more cancerous areas and if they have grown into the colon wall. If possible, any cancerous areas will be removed during this outpatient procedure.
- If the cancer was found closer to or in the rectum, a proctoscopy may be needed. An ultrasound probe is gently placed into the rectum. It emits inaudible sound waves that reflect off the rectum and surrounding tissues. A computer interprets these echoes to generate an image, which can reveal the depth of a rectal tumor or determine if the cancer has spread.
Imaging Tests After a Colorectal Cancer Diagnosis
If cancer is found, imaging tests may be necessary
- CT scan: You may receive an injection of contrast dye that makes it easier to see if cancer has spread to the liver, lungs, or other organs.
- Endorectal MRI scan: The doctor may want to get a better view of the pelvis in an MRI scan to see if cancer has spread to any of the nearby organs.
- PET-CT Scan: This nuclear medicine test will identify whether cancer has spread to other areas of the body, even if it can’t be seen with the eye yet.
- Angiography: If cancer has spread to the liver, this x-ray test shows the arteries that supply blood to those tumors, allowing the surgeon to determine if removal is possible.
Blood Tests After a Colorectal Cancer Diagnosis
- Tumor markers: Your doctor checks for carcinoembryonic antigen (CEA), a tumor marker, and other substances in the blood. Some people who have colorectal cancer or other conditions have a high CEA level.
- Complete blood count (CBC): This test reviews all of the various cell types in your blood, including red and white blood cells. A low red blood cell count is often found if a colorectal tumor is bleeding internally.
- Liver enzymes: This test indicates whether cancer may have spread to the liver. If liver enzymes are elevated, additional imaging may be done to look for cancer.
Molecular Testing of Colorectal Cancer Cells
The following tests are typically performed if the cancer is advanced or has recurred.
- Biomarker testing: If the biopsy shows advanced cancer, the cells are tested for specific gene and protein changes. Gene mutations associated with colorectal cancer include the KRAS, NRAS, and BRAF genes. If these genes test negative, a HER2 test may be run to see if too much HER2 protein is present, which causes colon cancer to grow.
- MSI and MMR testing: Colorectal cancer cells may also be tested for high levels of gene changes called microsatellite instability (MSI) or alterations in mismatch repair (MMR) genes. Understanding the genetic makeup of the tumor helps determine if targeted therapy or immunotherapy drugs could be options for treatment.
If you were recently diagnosed with colon or rectal cancer, New York Oncology Hematology provides state-of-the-art GI cancer care in the Albany area.