18F-FLT PET/CT as a Prognostic Imaging Biomarker of Disease-Specific Survival in Patients with Primary Soft-Tissue Sarcoma.

The purpose of this study was to evaluate 18F-FLT PET/CT as an early prognostic imaging biomarker of long-term overall survival and disease-specific survival (DSS) in soft-tissue sarcoma (STS) patients treated with neoadjuvant therapy (NAT) and surgical resection. Methods: This was a 10-y follow-up of a previous single-center, single-arm prospective clinical trial. Patients underwent 18F-FLT PET/CT before treatment (PET1) and after NAT (PET2). Posttreatment pathology specimens were assessed for tumor necrosis or fibrosis and for Ki-67 and thymidine kinase 1 expression. Maximally selected cutoffs for PET and histopathologic factors were applied. Survival was calculated from the date of subject consent to the date of death or last follow-up. Results: The study population consisted of 26 patients who underwent PET1; 16 of the 26 with primary STS underwent PET2. Thirteen deaths occurred during a median follow-up of 104 mo. In the overall cohort, overall survival was longer in patients with a low than a high PET1 tumor SUVmax (dichotomized by an SUVmax of ≥8.5 vs. <8.5: not yet reached vs. 49.7 mo; P = 0.0064). DSS showed a trend toward significance (P = 0.096). In a subanalysis of primary STS, DSS was significantly longer in patients with a low PET1 tumor SUVmax (dichotomized by an SUVmax of ≥8 vs. <8; P = 0.034). There were no significant 18F-FLT PET response thresholds corresponding to DSS or overall survival after NAT at PET2. Conclusion:18F-FLT PET may serve as a prognostic baseline imaging biomarker for DSS in patients with primary STS.