Among patients with Ewing sarcoma, functional imaging with 18fluorodeoxyglucose (FDG)–PET was a better predictor of response 9 days after the start of therapy than anatomic imaging ­modalities were at 6 weeks, results of a retrospective analysis suggest.

A study comparing the predictive ability of functional imaging modalities such as FDG-PET with that of anatomic imaging modalities such as CT or MRI showed that an early signal with FDG-PET was superior to anatomic imaging, and that newly defined tumor volume criteria were better at predicting response and clinical benefit than either World Health Organization (WHO) criteria or Response Evaluation Criteria in Solid Tumors (RECIST), reported Vadim S. Koshkin, MD, of the Cleveland Clinic and colleagues.

“The time needed to assess tumors volumetrically is slightly greater than to do so unidimensionally or bidimensionally, but the process is now automated. The analysis presented here suggests that assessment of tumor volume is superior to predict response in clinical trials, compared with the currently widely used RECIST and WHO criteria. This requires additional validation with prospective clinical trials,” they wrote (J Clin Oncol. 2016 Aug 29. doi: 10.1200/JCO.2016.68.1858 ].

To get a better idea of the relative benefits of FDG-PET and anatomic imaging for assessing clinical outcomes, the investigators took a retrospective look at patients with Ewing sarcoma who were enrolled in the SARC 011 trial , a single-arm, multicenter, multicohort phase II study of patients with recurrent Ewing sarcoma treated with the investigational insulinlike growth factor–1 receptor antibody R1507.

Of the 115 patients enrolled, 76 had available anatomic imaging at baseline and at 6 weeks after the start of treatment. The imaging studies were assessed by the treating oncologist according to WHO criteria and by a central, external group of radiologists blinded to clinical outcomes of individual patients. FDG-PET studies were performed at baseline and on day 9 and were assessed by central reviewers using PET Response Criteria in Solid Tumors (PERCIST).

The authors compared PERCIST 1.0 criteria for functional imaging with FDG-PET, and for anatomic imaging, WHO and RECIST criteria were assessed independently, and newly defined volumetric criteria were based on measurements done by the central radiology group using semi-automated solid tumor segmentation software.

As noted before, the investigators found results of day 9 FDG-PET scans were associated with reduced overall survival (OS) in patients with disease progression, compared with those without progression (P = .001), and with improved OS among patients with responses to the antibody, compared with those without responses.

“There was no significance in median survival between patients who responded to treatment and patients with stable disease for any of the imaging criteria. However, for all of the criteria, there was a trend toward longer survival for patients in the response group, compared with the stable disease group,” the authors wrote.

They found that the anatomic imaging criteria (WHO local and centralized assessments, RECIST, and volume) identified fewer patients in the response group than PERCIST (FDG-PET) criteria did.

When they looked at the subgroup of 66 patients who had both interpretable functional and anatomic imaging, they found that PERCIST identified 43.9% of patients as responders, and 90.9% as nonprogressors.

The authors acknowledged that their study was hampered by the retrospective design, small sample size relative to the trial population, and lack of FDG-PET standardization to common criteria across the treatment centers.