title: The predictive value of metabolic response to preoperative radiochemotherapy in locally advanced rectal cancer measured by PET/CT.
abstract: BACKGROUND
  To evaluate the value of positron emission tomography using fluorodeoxyglucose and computer tomography scan (FDG-PET/CT) for prediction of histopathological response of preoperative radiochemotherapy (RCTX) in patients with rectal carcinoma.
  
  
  METHODS
  Thirty patients with uT3 rectal carcinoma were examined by FDG-PET/CT at baseline, 14 days after initiation, and after completion of preoperative RCTX. The FDG decreases seen with PET scanning from baseline to day 14 (early metabolic response) and after completion of therapy (late metabolic response) were compared with histopathological tumor response. One patient denied surgery after RCTX.
  
  
  RESULTS
  The mean (+/-SD) reduction of tumor FDG uptake in histopathologically responding compared to non-responding tumors was -44.3% (+/-20.1%) versus -29.6% (+/-13.1%) (p = 0.085) at day 14 and -66.0% (+/-20.3%) versus -48.3% (+/-23.4%) (p = 0.040) after completion of RCTX. Best differentiation of histopathological tumor response was achieved by a cut-off value of 35% reduction of initial FDG uptake at day 14 and 57.5% after completion of therapy. Applying the cut-off values as a criterion for metabolic response, histopathological response was predicted with a sensitivity of 74% (14/19) at day 14 and 79% (15/19) after completion of therapy. The positive predictive value for early metabolic response was 82% (14/17) and for late metabolic response was 83% (15/18). Histopathological evidence of accumulated peritumoral inflammation cells was associated with a minor FDG decrease in five histopathologically responding patients, and influenced the results with negative predictive values of 58% (7/12) and 64% (7/11) at the early and late time points, respectively.
  
  
  CONCLUSIONS
  Metabolic response to a preoperative RCTX using FDG-PET/CT in rectal cancer patients can be correlated with histopathological response, but FDG uptake of peritumoral inflammation cells limited the results and led to false negative results.
authors.affiliation: Chirurgische Klinik und Poliklinik, Klinikum rechts der Isar der Technischen Universität München, Ismaningerstr. 22, 81675, Munich, Germany. Dr.Robert.Rosenberg@t-online.de
authors.forename: Robert
authors.initials: R
authors.lastname: Rosenberg
authors.forename: Ken
authors.initials: K
authors.lastname: Herrmann
authors.forename: Ralf
authors.initials: R
authors.lastname: Gertler
authors.forename: Beat
authors.initials: B
authors.lastname: Künzli
authors.forename: Markus
authors.initials: M
authors.lastname: Essler
authors.forename: Florian
authors.initials: F
authors.lastname: Lordick
authors.forename: Karen
authors.initials: K
authors.lastname: Becker
authors.forename: Tibor
authors.initials: T
authors.lastname: Schuster
authors.forename: Hans
authors.initials: H
authors.lastname: Geinitz
authors.forename: Matthias
authors.initials: M
authors.lastname: Maak
authors.forename: Markus
authors.initials: M
authors.lastname: Schwaiger
authors.forename: Jörg-Rüdiger
authors.initials: JR
authors.lastname: Siewert
authors.forename: Bernd
authors.initials: B
authors.lastname: Krause
mesh_terms: D019160:Endosonography; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D011237:Predictive Value of Tests; D011300:Preoperative Care; D012372:ROC Curve; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology / Q000628:therapy; D014057:Tomography, X-Ray Computed
chemical_list: D019788:Fluorodeoxyglucose F18