title: Value of FDG-PET for monitoring treatment response in patients with advanced GIST refractory to high-dose imatinib. A multicenter GEIS study.
abstract: OBJECTIVE
  The aim of this study was to evaluate the utility of positron emission tomography with 18F-fluorodeoxyglucose (FDG-PET) in monitoring response in refractory GIST.
  
  
  METHODS
  This multicenter study prospectively evaluated 21 patients with locally advanced and/or metastatic GIST refractory to with high-dose imatinib (800 mg/day) treated with doxorubicin 15-20 mg/m2/weekly for 4 cycles, followed by imatinib maintenance (400 mg/day). CT and FDG-PET were performed at baseline and after completion of therapy.
  
  
  RESULTS
  Mean baseline tumor size on CT was 5.9 cm. Median progression-free survival (PFS) was 219 days (range 62-1108). Three out of 21 patients (14%) had partial responses (PR) under RECIST criteria, 12 patients (57%) remained stable (SD) and 6 showed progression (PD) of the disease during treatment (29%). Six patients had PR by FDG-PET, 15 showed SD (n=9) or PD (n=6) based on EORTC criteria. Patients with a PFS <6 mo showed a significantly higher ∑SUVmax at baseline (26.04±13.4) than those with PFS≥6 mo (9.82±5.0) (P<0.05). A correlation was found between PET response and PFS: PR 14±6.1 mo, SD 5.5±0.8 mo and PD 3.5±4.1 mo (P<0.05). A residual SUVmax <5 after treatment correlated with improved PFS (314±315 days vs 131±91 days) (P<0.01). Survival curves showed a significant association between PET response and PFS (P<0.05). Patients with wild-type genotype KIT (KIT-WT) showed a significantly lower baseline SUVmax (5.36±1.4) than non-WT KIT (8.40±3.6) (P<0.05).
  
  
  CONCLUSIONS
  FDG-PET is useful in assessing response of GIST refractory to imatinib and correlates with the presence of KIT-WT. Baseline ∑SUVmax can predict response to treatment in this series.
authors.affiliation: Nuclear Medicine, Hospital Clínic Barcelona, Barcelona, Spain. dfuster@clinic.ub.es
authors.forename: D
authors.initials: D
authors.lastname: Fuster
authors.forename: J R
authors.initials: JR
authors.lastname: Ayuso
authors.forename: A
authors.initials: A
authors.lastname: Poveda
authors.forename: R
authors.initials: R
authors.lastname: Cubedo
authors.forename: A
authors.initials: A
authors.lastname: Casado
authors.forename: J
authors.initials: J
authors.lastname: Martínez-Trufero
authors.forename: A
authors.initials: A
authors.lastname: López-Pousa
authors.forename: X G
authors.initials: XG
authors.lastname: Del Muro
authors.forename: F
authors.initials: F
authors.lastname: Lomeña
authors.forename: J
authors.initials: J
authors.lastname: Maurel
authors.forename: F
authors.initials: F
authors.lastname: Pons
mesh_terms: D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000627:therapeutic use; D001549:Benzamides; D005260:Female; D019788:Fluorodeoxyglucose F18; D046152:Gastrointestinal Stromal Tumors; D006801:Humans; D000068877:Imatinib Mesylate; D008297:Male; D008875:Middle Aged; D010879:Piperazines / Q000627:therapeutic use*; D049268:Positron-Emission Tomography / Q000379:methods*; D011743:Pyrimidines / Q000627:therapeutic use*; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013030:Spain; D016896:Treatment Outcome
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D010879:Piperazines; D011743:Pyrimidines; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D000068877:Imatinib Mesylate