Early Evaluation of Response Using 18 F-FDG PET Influences Management in Gastrointestinal Stromal Tumor Patients Treated with Neoadjuvant Imatinib.

18 F-FDG PET has previously been proven effective as an early way to evaluate the response of gastrointestinal stromal tumors (GISTs) to imatinib treatment. However, it is unclear whether early evaluation of response affects treatment decisions in GIST patients treated with neoadjuvant intent. Methods: We retrospectively scored changes in management based on early evaluation of response by 18 F-FDG PET in patients in the Dutch GIST registry treated with neoadjuvant imatinib. Results: Seventy 18 F-FDG PET scans were obtained for 63 GIST patients to evaluate for an early response to neoadjuvant imatinib. The scans led to a change in management in 27.1% of the patients. Change in management correlated strongly with lack of metabolic response ( P < 0.001) and non- KIT exon 11-mutated GISTs ( P < 0.001). Conclusion: Performing 18 F-FDG PET for early evaluation of response often results in a change of management in GIST patients harboring the non- KIT exon 11 mutation and should be considered the standard of care in GIST patients treated with neoadjuvant intent.