Hence, it is important to recognize that such polyps can be found incidentally with PET/CT and need to be investigated further by colonoscopy.
Aside from normal colonic uptake of FDG, both benign and malignant colonic lesions can be detected by FDG-PET. A study by Yasuda et al. looked at 110 patients and found that precancerous adenomatous polyps can be detected incidentally on whole body images performed for other indications with a sensitivity of 24%.
PET/CT is usually not used for diagnosing colorectal cancer. Rather, PET/CT most often is used to determine the extent of cancer (staging) after cancer has been diagnosed. PET/CT is also frequently used for re-staging after treatment. PET/CT is the most powerful and accurate tool available for those two tasks.
Fifty eight patients had false negative PET scans but colonoscopy revealed true pre-malignant and malignant pathology, yielding 23% sensitivity. The specificity, negative predictive value (NPV) and accuracy were 96%, 90% and 87%, respectively.
Colonoscopy is one of the most sensitive tests currently available for colon cancer screening. The doctor can view your entire colon and rectum. Abnormal tissue, such as polyps, and tissue samples (biopsies) can be removed through the scope during the exam.
Stool tests.
Both polyps and colorectal cancers can bleed, and stool tests check for tiny amounts of blood in feces (stool) that cannot be seen visually. (Blood in stool may also indicate the presence of conditions that are not cancer, such as hemorrhoids.)
Other Options: The FIT Test and Cologuard
If you are not ready for a colonoscopy, the next best option is a Fecal Immuno-histochemistry test (FIT), which can detect about 80% of problems. This test is done in the convenience your home, and requires no preparation, time off from work, or sedation.
PET scanning can give false results if chemical balances within the body are not normal. Specifically, test results of diabetic patients or patients who have eaten within a few hours prior to the examination can be adversely affected because of altered blood sugar or blood insulin levels.
How is PET used for colorectal cancer? Physicians use PET-CT studies to: diagnose and stage: by determining the exact location of a tumor, the extent or stage of the disease and whether the cancer has spread in the body.
Previous studies have indicated that PET has a high sensitivity (90%) and specificity (66%) for identifying primary colorectal tumors (2), and FDG-PET provides a sensitivity of 90% for detecting metastatic liver lesions, with a specificity of 100% (1).
Not all cancers show up on a PET scan. PET scan results are often used with other imaging and lab test results. Other tests are often needed to find out whether an area that collected a lot of radioactive material is non-cancerous (benign) or cancerous (malignant).
For some types of cancer, a PET-CT scan is a way to help find cancer and learn its stage. Stage is a way to describe where the cancer is and if it has spread. Doctors also learn information about the stage if and how the cancer is affecting your body's functions.
A gastroenterologist, the specialist who usually performs a colonoscopy, can't tell for certain if a colon polyp is precancerous or cancerous until it's removed and examined under a microscope.
Most polyps are benign (not cancerous). Your doctor can tell if a colon polyp is cancerous during a colonoscopy by collecting tissue to biopsy. The results of the biopsy are typically sent to your doctor within a week.
If a polyp has cancerous cells, they will also biopsy nearby lymph nodes to determine if the cancer has spread or metastasized to other areas of the body. In this case radiation, chemotherapy or other therapies may be recommended. Colonoscopy screenings can be life saving!
PET scans can help detect cancer and how far it has spread. PET scans can show solid tumors in the brain, prostate, thyroid, lungs, and cervix. The scans can also evaluate the occurrence of colorectal, lymphoma, melanoma, and pancreatic tumors.
PET/CT is believed to be the most accurate imaging test available to evaluate lung cancer, colon cancer, breast cancer, melanoma, lymphoma, head and neck cancer, and esophageal cancer. In published research studies, PET has been shown to have an approximately 90% accuracy in many of these cancer types.
Unlike a PET scan, which focuses on cellular-level activities, an MRI produces images of organs and structures. MRIs help diagnose problems in many areas, and are most commonly used to evaluate: Joints (including wrists, ankles, knees, and back) Blood vessels.
PET scans are more accurate than biopsy for cancer diagnosis. They can detect very small tumors that would not be detectable on a biopsy.
In general, PET scans may be used to evaluate organs and/or tissues for the presence of disease or other conditions. PET may also be used to evaluate the function of organs, such as the heart or brain. The most common use of PET is in the detection of cancer and the evaluation of cancer treatment.
Studies show that, for someone of average risk, the FIT test is a good alternative to colonoscopy. There is also evidence that people unwilling to undergo a colonoscopy will complete a FIT test.
In conclusion, CT colonography detects most large polyps but performs less well for smaller lesions.