PET makes inroads in abdominal cancer imaging

PET/CT is proving to be an excellent imaging modality in patients with gastrointestinal cancers, potentially replacing endoscopy and barium studies.

Endoscopy retains an important place in routine clinical practice, particularly in the diagnosis and management of esophageal, gastric, and colon cancers. But it is invasive, risky, and expensive, according to Dr. Abass Alavi, emeritus chair of the nuclear medicine department at the University of Pennsylvania. Even barium enemas, which are relatively safe, pose some disadvantages, especially discomfort.

In many cases, these tests may not be able to display the full extent of disease, either locally or regionally. Additionally, many patients have to undergo more than one of these exams, reducing their cost-effectiveness. Using PET, at least after the initial diagnosis, to stage disease, monitor treatment response, or detect recurrence could one day prove a more cost-effective way to go, Alavi said.

"PET is a powerful technology, certainly cost-effective. And with the addition of CT, which is now more commonly used than PET alone, it combines the best of both worlds. The abdomen, which presents complex anatomies and processes, is one area of the body where we clearly believe that PET or PET/CT should be the modality of choice," he said.

Studies are emerging attesting to PET's efficacy in GI cancers. Dr. Bernd Krause, a nuclear medicine physician, and colleagues at the Technical University of Munich in Germany prospectively evaluated 71 patients with gastric cancer who underwent FDG-PET at baseline and 14 days after beginning chemotherapy. The investigators determined that a reduction of 35% or more in FDG uptake would indicate that patients were having a positive metabolic response to treatment. They reported their results at the 2007 Society of Nuclear Medicine meeting.

Sixteen patients met the FDG uptake threshold for metabolic response. They showed a histopathological response rate of 65% and a median survival of 56 months. Thirty-two patients who were nonmetabolic responders showed a biopsy-proven response rate of 17% and a median survival of 24 months. Poor FDG uptake in the nonresponders could be correlated to high mucus content or other physiologic features of the affected area, Krause said.

Researchers also observed 22 patients with negative FDG uptake but with a histopathological response rate of 21% and a median survival of 36 months. The negative responders and nonresponders showed no significant difference in terms of biopsy-recorded treatment response and survival. Krause concluded that nonresponding patients and PET-negative patients with low histopathological response should undergo immediate resection or a change in their chemotherapy regimens.

In another study, Dr. Barry Chatterton, director of nuclear medicine and bone densitometry at Royal Adelaide Hospital in South Australia, and colleagues assessed 129 patients with gastroesophageal cancer using FDG-PET. The technique helped change management in almost 40% of patients, all of whom had already been assessed with conventional imaging.

PET provides a highly significant prediction of disease progression, Chatterton said. The number of patients slated for palliative treatment increased from 10 pre-PET to 32 post-PET. And 34% of patients with a curative management plan had to be upstaged and treated palliatively instead after PET results.