Colorectal cancer is the third most common cancer in both men and women. According to the American Cancer Society, each year there are an estimated 101,000 colon and 40,000 rectal cancer cases diagnosed in the U.S., with an estimated 49,000 deaths, for about 9% of cancer deaths. Incidence and mortality rates continue to decline in both men and women, reflecting earlier detection through increased screening and improvements in diagnosis and treatment.
Early diagnosis of this disease is one of the key elements to its cure. Colorectal cancers probably develop slowly over a period of several years. Before a true cancer develops, there are often earlier changes in the lining of the colon or rectum. If disease is found early, before colorectal cancer has spread, it is considered curable. However, as the tumor spreads to involve adjacent organs or lymph nodes, a patient's five-year survival rate drops to 68%. If the cancer has already spread to distant organs, the long-term survival rate decreases substantially.
Colorectal Cancer Diagnosis
Over 95% of colon and rectal cancers are adenocarcinomas, a type of cancer of the cells that are on the inside lining of the colon and rectum. Polyps form on the lining and lead to cancer. Colon cancer can be prevented if these polyps are detected and removed. Recently, screening methods have been recommended for people without symptoms to try to find either the polyps or early signs of cancer. In many cases, screening tests can find colorectal cancers at an early stage and greatly improve the chances of successful treatment. Beginning at age 50, men and women who are at average risk for developing colorectal cancer should begin screening.
Screening tests include:
- Physical exam - as a part of your routine visit to your physician
- Fecal occult blood test - take home kits that test multiple stool samples
- Sigmoidoscopy/colonoscopy - an X-ray procedure in which a scope is inserted inside the colon to look for changes or polyps that might be a precursor to cancer
- Barium enema - an X-ray procedure that takes pictures of the colon
Many colon cancers have no symptoms. Hidden blood in the stool is often the only warning sign of colon cancer. The following symptoms can be associated with colon and rectal cancer:
- Change in bowel habits such as diarrhea, constipation, or narrowing of the stool that lasts for more than a few days
- Feeling that you need to have a bowel movement that doesn't go away after doing so
- Loss of weight
- Constant tiredness
- Bleeding from the rectum or blood in the stool
- Cramping or tenderness in the abdomen
- Unexplained low blood counts
- Bowel obstruction
If colon cancer is suspected, further tests are ordered to find out if the disease is really present and to see if it has spread. A biopsy procedure, which may be done as part of a colonoscopy, can determine if cancer is present. The physician may order a series of blood tests to look for substances like CEA and CA-19-9 that are made by colon and rectal cancer cells and released into the blood stream. In cases of suspected or known colon cancer, the physician may also order a CT scan to show the structure of the organs and tissues in the abdomen. While these tests can provide information regarding the size and location of the primary tumor and may be able to detect other abnormalities that may represent the spread of the disease, they cannot tell if the abnormalities are benign or cancerous.
PET/CT scanning is an important addition to other tests that can be done right after you are diagnosed with cancer of the colon or rectum.
Source: American Cancer Society. Cancer Facts & Figures 2011. Atlanta: American Cancer Society; 2011
Colorectal Cancer Treatment
Doctors diagnose cancer and determine its origin by looking at a sample of the tumor under a microscope. Then, before deciding on a treatment strategy, physicians must determine if or how much the colon cancer has spread. This is called "staging".
In colon cancer, staging reflects how far into the colon the tumor has grown and whether or not it has spread beyond it, either to the lymph nodes or to distant organs. The prognosis or the patient's outlook for recovery and determining the best treatment options depend upon the stage of the cancer. For early cancer, surgery may be all that is needed. For cancer that is more advanced, chemical or radiation therapy may be needed as well to increase the chance of a cure or delay the cancer's progression.
A PET/CT scan will image the entire body and will show by uptake of the radioactive glucose if the cancer has affected the nearby lymph nodes or other more distant sites. Whether or not distant organs are involved is a critical factor in deciding what the surgical and medical treatment will be. Some studies have shown that even if the cancer is spread in a limited way outside the colon, surgery can be done to remove these other tumors and improve the chance of recovery.
A PET/CT scan can help the physician determine whether surgery, chemotherapy or radiation therapy is the best treatment option.
Colorectal Cancer Follow-up
For several years after treatment, it is important to have regular follow-up examinations to determine if any active cancer cells have returned. Physical and rectal exams by a physician, regular colonoscopy, and blood tests are important to help tell if the cancer has come back. Blood markers like CEA are present in some patients with active colon cancer, so a rise in these blood values is used as an early warning sign that the cancer has returned. However, some people without cancer also have CEA in their blood, so it cannot be used as a specific test for cancer.
Imaging with PET/CT is also critical in order to look for the return of the cancer. Other imaging tests might not detect the cancer, which could result in a delay of further treatment. In many patients with colorectal cancer, a mass may develop in the pelvis. The mass can be seen on a CT scan, but CT cannot determine if it is the result of surgical or radiation scarring or if it is a recurrent cancer that must be treated. If the mass is cancerous, it will demonstrate increased uptake of the radioactive glucose on the PET/CT scan. If, however, the mass is because of scarring caused by the radiation treatments, no glucose uptake will be seen in the abnormality.
PET/CT can be used to image tumor response to therapy and to detect recurrence in treated lesions. After surgery and other treatments, PET/CT is extremely important for monitoring to see if the cancer cells have returned and if treatment should be restarted.
PET/CT can be used to image colorectal cancer response to therapy and to detect recurrence in treated lesions.
Colorectal Cancer PET/CT Utilization
PET/CT is a noninvasive test that physicians utilize to stage the body for the presence or absence of active tumor, localize the tumor, assess the tumor response to treatment, and detect recurrence in treated lesions.
Colorectal Cancer Indications
- Detecting tumor recurrence in patients with rising levels of serum CEA and otherwise normal radiographic studies
- Determining if a radiological abnormality is a resectable recurrence, its true extent, and if it has metastasized elsewhere
- Detecting intra-abdominal, hepatic or other metastases
- Detecting extrahepatic metastases before a potentially curable hepatic resection
- Evaluating efficacy of treatment, such as chemotherapy and radiation
- Evaluating response to treatment
Source: Atlas of Clinical Positron Emission Tomography by Sallie F. Barrington, Michael N. Maisey and Richard R. Wahl. Oxford University Press, Inc. New York, NY.