title: Extra-thoracic tumor burden but not thoracic tumor burden on (18)F-FDG PET/CT is an independent prognostic biomarker for extensive-disease small cell lung cancer.
abstract: OBJECTIVE
  The aim of this study was to evaluate the relationship and difference in prognostic significance between whole-body tumor burden, thoracic tumor burden, and extra-thoracic tumor burden on (18)F-FDG PET/CT for patients with extensive-disease small cell lung cancer (ED-SCLC).
  
  
  METHODS
  We performed a retrospective, two-center analysis for patients with ED-SCLC who underwent pretreatment (18)F-FDG PET/CT. Metabolic tumor burden was estimated using whole-body metabolic tumor volume (MTV(WB)), thoracic metabolic tumor volume (MTV(TRX)), extra-thoracic metabolic tumor volume (MTV(EXT)), and the number of extra-thoracic tumor foci. Uni- and multivariate analyses were performed using various clinical factors and the metabolic indices.
  
  
  RESULTS
  A total of 91 patients were eligible for this study. MTV(WB) showed stronger correlation with MTV(EXT) than MTV(TRX) (r(2) = 0.804 vs. 0.132, p < 0.001, both), whereas no correlation was observed between MTV(EXT) and MTV(TRX) (r(2) = 0.007, p = 0.428). Patients with smaller MTV(WB), MTV(EXT), and extra-thoracic tumor foci showed longer survival than patients with larger MTV(WB), MTV(EXT), and extra-thoracic tumor foci, respectively, whereas the survival difference between patients with smaller MTV(TRX) and those with larger MTV(TRX) was not significant. Results of uni- and multivariate analyses showed that ECOG performance status (HR = 2.31, p = 0.015), initial chemotherapy cycles (HR = 0.24, p < 0.001), and the number of extra-thoracic tumor foci (HR = 2.75, p < 0.001) were independent prognostic factors for overall survival, and initial chemotherapy cycles (HR = 0.25, p < 0.001), and MTV(EXT) (HR = 2.04, p = 0.013) were independent prognostic factors for progression-free survival.
  
  
  CONCLUSIONS
  These data provide evidence indicating that extra-thoracic tumor burden but not thoracic tumor burden is an independent prognostic biomarker for ED-SCLC, and support further exploration of novel treatment strategies targeting extra-thoracic tumor burden in order to improve the clinical outcomes of patients with ED-SCLC.
authors.affiliation: Department of Nuclear Medicine, Kyungpook National University Hospital, Daegu, Republic of Korea.
authors.forename: Jong-Ryool
authors.initials: JR
authors.lastname: Oh
authors.forename: Ji-Hyoung
authors.initials: JH
authors.lastname: Seo
authors.forename: Chae Moon
authors.initials: CM
authors.lastname: Hong
authors.forename: Shin Young
authors.initials: SY
authors.lastname: Jeong
authors.forename: Sang-Woo
authors.initials: SW
authors.lastname: Lee
authors.forename: Jaetae
authors.initials: J
authors.lastname: Lee
authors.forename: Jung-Joon
authors.initials: JJ
authors.lastname: Min
authors.forename: Ho-Chun
authors.initials: HC
authors.lastname: Song
authors.forename: Hee-Seung
authors.initials: HS
authors.lastname: Bom
authors.forename: Young-Chul
authors.initials: YC
authors.lastname: Kim
authors.forename: Byeong-Cheol
authors.initials: BC
authors.lastname: Ahn
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018572:Disease-Free Survival; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008175:Lung Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography / Q000379:methods; D011379:Prognosis; D019275:Radiopharmaceuticals; D012189:Retrospective Studies; D055752:Small Cell Lung Carcinoma / Q000175:diagnosis* / Q000000981:diagnostic imaging* / Q000473:pathology; D013899:Thoracic Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging* / Q000473:pathology; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
keywords: (18)F-FDG PET/CT; Biomarker; Extensive disease small cell lung cancer; Metabolic tumor volume; Oligometastases; Prognosis