title: Gastrointestinal stromal tumors treated with imatinib mesylate: apparent diffusion coefficient in the evaluation of therapy response in patients.
abstract: OBJECTIVE
  To prospectively investigate the use of the apparent diffusion coefficient (ADC) as an early response indicator in patients with gastrointestinal stromal tumors (GISTs) treated with imatinib mesylate.
  
  
  METHODS
  This study was approved by the institutional review board and written informed consent was obtained from all patients. Diffusion-weighted magnetic resonance (MR) imaging was performed in 32 patients with GISTs before and 1, 4, and 12 weeks after treatment with a tyrosine kinase inhibitor, imatinib mesylate. The measurable lesions were classified as having responded well or poorly according to size alterations at clinical evaluation following the first round of treatment (3 months). A linear mixed-effects model was applied to analyze changes in the ADCs of tumors during treatment and to compare the variation and slopes of the time-dependent ADC curves between the good- and poor-response groups.
  
  
  RESULTS
  There were 56 lesions in the good-response group and 35 in the poor-response group. An early (1 week after therapy) noticeable and statistically significant (P < .001) increase in the ADC was observed in the good-response group (median ADC increase, 44.8%) but not in the poor-response group (median ADC increase, 1.5%). The time-dependent ADC variation was significantly different between the good- and poor-response groups, with a sharper median ADC increase displayed in the former (week 1: 44.8% vs 1.5%; week 4: 80.4% vs 7.8%; week 12: 89.6% vs 16.7%; F = 25.78, P < .001). The largest difference in the weekly percentage increase in ADC between the good- and poor-response groups was observed at 1 week after therapy (week 0-1: 44.8% vs 1.5%; week 1-4: 7.0% vs 2.8%; week 4-12: 1.6% vs 0.7%). The pretherapy mean ADC (± standard deviation) of lesions in the good-response group (1.06 [×10(-3) mm(2)/sec] ± 0.27) was significantly lower than that in the poor-response group (1.24 [×10(-3) mm(2)/sec] ± 0.32) (F = 8.34, P = .005).
  
  
  CONCLUSIONS
  Comparatively low pretherapy ADC and marked ADC increase at 1 week after therapy is associated with good response to imatinib mesylate in patients with GISTs.
authors.affiliation: Key Laboratory of Carcinogenesis and Translational Research, Department of Radiology, Peking University School of Oncology, Beijing Cancer Hospital & Institute, No. 52 Fu Cheng Road, Hai Dian District, Beijing 100142, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Tang
authors.forename: Xiao-Peng
authors.initials: XP
authors.lastname: Zhang
authors.forename: Ying-Shi
authors.initials: YS
authors.lastname: Sun
authors.forename: Lin
authors.initials: L
authors.lastname: Shen
authors.forename: Jian
authors.initials: J
authors.lastname: Li
authors.forename: Li-Ping
authors.initials: LP
authors.lastname: Qi
authors.forename: Yong
authors.initials: Y
authors.lastname: Cui
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001549:Benzamides; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D046152:Gastrointestinal Stromal Tumors / Q000188:drug therapy* / Q000473:pathology*; D006801:Humans; D000068877:Imatinib Mesylate; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D010879:Piperazines / Q000627:therapeutic use*; D011446:Prospective Studies; D011743:Pyrimidines / Q000627:therapeutic use*; D016896:Treatment Outcome
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate