PROGNOSTIC ROLE OF PET IN SARCOMAS

What at least one investigator has been saying for nearly 2 decades is supported by a new study: ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) can provide important prognostic information about soft-tissue and bone sarcomas.

In a systematic review and meta-analysis of six studies that included more than 500 patients with sarcomas of soft tissue and bone, patients who had tumors in which the maximum standardized uptake value (SUVmax) of ¹⁸F-FDG was high had a 22% higher risk for poor outcomes compared with patients whose tumors had low SUVmax, reported Tadahiko Kubo, MD, and colleagues from Hiroshima University, in Japan.

Although some studies have reported that SUVmax, a semiquantitative measure, is useful for predicting survival in patients with soft-tissue and bone sarcomas, others have reported conflicting results.

Furthermore, other studies have suggested that other PET-derived measures, such as total lesion glycolysis or tumor texture analysis, can provide more useful prognostic information than SUVmax.

Those alternative measures, however, are "higher-order metrics" that require additional image segmentation and postprocessing. Additionally, studies have been limited by small numbers of patients, owing to the rarity of sarcomas, the investigators note.

"Therefore, we conducted a meta-analysis to derive more robust estimates of predictive performance of ¹⁸F-FDG PET, which to our knowledge had not been studied previously," they write. The study was published in the May issue of the European Journal of Cancer.

The investigators trolled systematically through large medical literature databases and ultimately identified six studies that met all of their criteria. The studies included data on a total of 514 patients with various soft-tissue and bone sarcoma histologies.

They found that the pooled hazard ratio (HR) for overall survival was 1.22 (95% confidence interval [CI], 1.03 - 1.46), an indicator that a high SUVmax can predict significantly shorter overall survival compared with low SUVmax (P = .03).

When the authors performed a subgroup analysis of patients with soft-tissue sarcomas only, they found a slightly less robust but still significant predictive effect for FDG-PET (P =.004), with a pooled HR of 1.15 (95% CI, 1.05 - 1.27). They noted, however, that this subanalysis included only two studies, with a total of 96 patients.

Their findings come as no surprise to Janet F. Eary, MD, professor of radiology and director of the Advanced Imaging Facility at the University of Alabama School of Medicine, in Birmingham.

Dr Eary has studied FDG-PET imaging and sarcomas since the late 1990s.

She and colleagues showed in a retrospective analysispublished in 2002 that in 209 patients with sarcoma who underwent FDG-PET imaging, SUVmax was a statistically significant independent predictor of patient survival and that tumors with higher SUVmax were associated with a significantly worse prognosis.

Dr Eary was a coauthor of a second study, published in 2005, that showed that in patients with soft-tissue sarcomas of the extremities, both SUVmax before neoadjuvant chemotherapy and change in SUVmax after chemotherapy independently identified patients at high risk for tumor recurrence.

"The FDG-PET scan showed promise as a tool to identify the patients with sarcoma who are most likely to benefit from chemotherapy," they wrote.

Interestingly, "when we validated that data, what it showed was that in the population we looked after, chemotherapy ― neoadjuvant chemotherapy ― actually had an effect," Dr Eary said in an interview with Medscape Medical News.

Despite those findings, neoadjuvant chemotherapy is still only sporadically used to treat sarcoma patients in the United States and Canada.

"We've never understood that," said Dr Eary, who was asked to comment.

Regarding the meta-analysis, Dr Eary said, "It's interesting, but sarcoma papers are notoriously difficult to collect and analyze, because usually the series are so small."

In addition, there were differences among the studies in how the imaging was performed, and there is a lack of data on how or whether the results were clinically validated.

"It might be that some of the messages of the ability [of FDG-PET] to predict survival or prognosticate is diluted by those factors," she said.

The study was supported by Practical Research for Innovative Cancer Control from the Japan Agency for Medical Research and Development and the Japan Society for Promotion of Science. The authors and Dr Eary have disclosed no relevant financial relationships.