Better Imaging Method for Ewing Sarcoma Response Assessment

Functional imaging using FDG-positron emission tomography (FDG-PET) was able to predict response to treatment in Ewing sarcoma patients, and was superior to other anatomic imaging criteria, according to a new retrospective analysis.

The criteria used to determine disease progression are not fully standardized, with differing volume increases used by WHO, SWOG, and RECIST; response criteria, however, are consistent across definitions. “A new methodology for estimation of change in volume throughout treatment could generate more accurate and objective criteria for the definition of progression and response,” wrote study authors led by Laurence H. Baker, DO, of the University of Michigan Medical School in Ann Arbor.

Though the use of FDG-PET has been increasing, comparisons to anatomic imaging as assessments for clinical outcome are lacking. The new study was a retrospective analysis of the 115 Ewing sarcoma patients in the SARC 011 trial treated with a novel IGF1 receptor antibody, comparing five different imaging criteria using both functional and anatomic imaging; of those, 89 had anatomic imaging available for review, and 92 had FDG-PET scans done at baseline and at day 9 of treatment (66 patients had both types of imaging available). The results of the analysis were published online ahead of print in the Journal of Clinical Oncology.

The use of functional imaging criteria, known as PERCIST, identified more patients who responded to the treatment than did any of the four anatomic imaging criteria (volume, WHO local, WHO central, RECIST). Among the 66 patients with interpretable functional imaging and anatomic imaging, 43.9% were responders according to PERCIST, and an average of 21.7% of patients were responders using the anatomic criteria. Those anatomic criteria produced a wide range of those deemed responders, from 21% to 35%, and those deemed progressors, from 12% to 50%.

“Use of PERCIST would lead to fewer patients discontinuing therapy,” the authors wrote, also noting that FDG-PET was performed much earlier in treatment and still identified more responders.

Those deemed progressors based on the FDG-PET scan at day 9 had a median overall survival of 5.5 months, compared with 13 months for those with a response and 11.4 months in those with stable disease. Patients with baseline anatomic imaging who did not also undergo week 6 imaging (13 patients) had reduced overall survival compared with those who underwent both imaging tests (P < .001).

“We showed that FDG-PET assessed by PERCIST as early as day 9 predicted clinical benefit of IGF1 receptor antibody in Ewing sarcoma,” the authors concluded. “FDG-PET was shown to be superior to any of the assessed anatomic imaging criteria in identification of response.”