According to results recently presented at the 2003 American Roentgen Ray Society Annual Meeting, a PET scan is significantly more accurate at detecting colon cancer metastasis than a CT scan.
Colorectal cancer is the second leading cause of cancer deaths in the United States. It is estimated that colorectal cancer will cause nearly 60,000 deaths in the U.S. in 2003. The colon and rectum are parts of the large intestine and cancer can spread locally or to distant sites in the body. Initially, if a patient is diagnosed with colon cancer that appears to have spread outside the tumor, CT (computed tomography) scans are often used to determine if and where in the body the cancer has spread. In addition, scans are also used to determine how a patient is responding to treatment, or as follow-up to determine if and where cancer has recurred. Researchers continue to evaluate what type of scans will produce the most accurate results for several types of cancer.
PET (positron emission tomography) scans are gaining acceptance as being more accurate than other scans for certain types of cancer. PET scans are able to distinguish between dead tissue and active cancer cells by exploiting a biological characteristic of rapidly dividing cancer cells – the metabolism of sugar. A solution containing a type of sugar attached to a radioactive compound is injected into the vein of a patient undergoing a PET scan. Cancer cells tend to take up more sugar than normal cells, so the solution becomes concentrated in the cancer. The attached radioactive compound emits a form of radiation that can be detected by the PET scanner. The scanner then forms a picture that allows the physician to see the location of small amounts of cancer cells if they exist.
Researchers from Philadelphia recently conducted a clinical study comparing the accuracy of PET and CT scans in the detection of cancer spread in patients with colon cancer. The study involved 35 patients, between the ages of 40 and 83, with various stages of colon cancer. PET scans identified 93% of metastatic areas of cancer, compared to only 46% for CT scans. False identification of cancer did not occur with PET scans, but occurred at a rate of 27% in CT scans. Overall accuracy (rate of cancers detected plus rate of false detections) was 93% for PET scans, and only 56% for CT scans.
These authors concluded that PET scans are significantly more accurate than CT scans at detecting cancer metastasis in patients with colon cancer, and should become part of initial staging and evaluation following therapy for these patients. Patients with colon cancer may wish to speak with their physician about the risks and benefits of PET scanning or the participation in a clinical trial further evaluating PET scans or other screening procedures.
Reference: Ahmed I, et al. Proceedings from the 2003 American Roentgen Ray Society Annual Meeting. California, 2003. Abstract #104