TUESDAY, Jan. 27, 2004 (HealthDayNews) -- When people with cancer have positron emission tomography (PET) scans to determine the spread of their disease, their doctors may find more some unwelcome surprises.
That's the conclusion of a new study in the February issue of Radiology, which found 58 suspected cancers in 1,750 scans of people believed to have cancer. What was shocking was that these suspected cancers weren't related to the original cancer, and most of the people had no apparent symptoms from the additional cancer.
"As we were evaluating routine PET scans in patients who had cancer, or who potentially had cancer, we found these unexpected abnormalities that you wouldn't expect to find with these tumors," says study author Dr. Harry Agress Jr., director of nuclear medicine and the PET center at Hackensack University Medical Center.
"We were able to identify cancers in patients who had no idea they were there," Agress says. "And they were picked up early enough that they could be removed before they spread."
PET scanning is done using small amounts of a slightly radioactive substance. Cells that use more energy absorb more of this substance, causing them to change colors on the scan. Cancerous cells often use more energy than normal cells. Areas of inflammation and infection can also use more energy, so PET scanning is often used in conjunction with other imaging techniques, such as CT scanning, to help doctors differentiate what's causing an area to change colors on a PET scan.
For this study, Agress and his colleague, Dr. Benjamin Cooper, reviewed PET scans done on people who were believed to have cancer. They discovered 58 abnormalities in 53 people out of 1,750 scans. These abnormalities were unrelated to the original reason these people were seeking treatment.
Agress says they waited about a month and then checked to be sure follow-up tests were done on the people with abnormalities. Forty-two people allowed the suspected cancerous cells to be biopsied.
"In patients who would allow a biopsy, 71 percent of the unexpected abnormalities were found to be either a cancerous or precancerous lesion," says Agress. "These abnormalities had nothing to do with why they had the scan and in the vast majority of cases, these people were completely asymptomatic."
"We're detecting things in patients that we did not know existed," says Dr. Jay Brooks, chief of hematology and oncology at Ochsner Clinic Foundation Hospital in New Orleans. But, he says, it's important to remember that PET scanning isn't 100 percent accurate, and that what's seen on a PET scan needs to be correlated with what else is going on in the body that might cause abnormal findings, such as an injury or infection.
Dr. Phil Evans, a spokesman for the American Cancer Society and a professor of radiology at the University of Texas Southwestern in Dallas, says these findings should be interpreted cautiously because these scans were done on a high-risk population. And, he adds, these findings need to be corroborated in other studies.
"PET is a very good tool in people who have or who are suspected of having cancer and it's a good staging tool, but it's not good for everyone," he says. Evans also points out that less than 2 percent of all the scans examined had unexpected abnormalities, so PET likely wouldn't make an efficient screening tool for the general population.
Agress says that it's hard to say if PET would ever be used for screening, particularly because of its cost -- around $1,800. He adds that some radiology centers are now using a combined CT/PET scanner that does both types of scans simultaneously, and may give doctors an even more effective way to diagnose cancer.
More information
To learn more about how cancer is detected, visit the National Cancer Institute or read this article from the American Cancer Society comparing PET scans to CT scans.
