title: Nodal staging in rectal cancer: why is restaging after chemoradiation more accurate than primary nodal staging?
abstract: OBJECTIVE
  This study aims to explore the influence of chemoradiation treatment (CRT) on rectal cancer nodes and to generate hypotheses why nodal restaging post-CRT is more accurate than at primary staging.
  
  
  METHODS
  Thirty-nine patients with locally advanced rectal cancer underwent MRI pre- and post-CRT. All visible mesorectal nodes were measured on a 3D T1-weighted gradient echo (3D T1W GRE) sequence with 1-mm(3) voxels and matched between pre- and post-CRT-MRI and with histology by lesion-by-lesion matching. Change in number and size of nodes was compared between pre- and post-CRT-MRI. ROC curves were constructed to assess diagnostic performance of size.
  
  
  RESULTS
  Eight hundred ninety-five nodes were found pre-CRT: 44 % disappeared and 40 % became smaller post-CRT. Disappearing nodes were initially significantly smaller than nodes that remained visible post-CRT: 2.9 mm vs. 3.8 mm. cN+ stage was predicted in 97 % pre-CRT and 36 % of patients had ypN+ post-CRT. ypN+ patients had significantly larger nodes than ypN0 patients both pre- and post-CRT. Optimal size cutoff for post-CRT ypN stage prediction was 2.5 mm (area under the curve (AUC) of 0.78) at MRI.
  
  
  CONCLUSIONS
  After CRT, most lymph nodes become smaller, and many disappear. Size predicts disappearance and node positivity. Together with a low prevalence of ypN+, this can explain the higher accuracy of nodal staging after CRT than in a primary staging setting, possibly of use when considering organ-preserving strategies after CRT.
authors.affiliation: Department of Radiology, Maastricht University Medical Center, Maastricht University, PO Box 5800, 6202, Maastricht, The Netherlands.|Department of Surgery, Maastricht University Medical Center, Maastricht University, PO Box 5800, 6202, Maastricht, The Netherlands.
authors.forename: Luc A
authors.initials: LA
authors.lastname: Heijnen
authors.affiliation: Department of Radiology, Maastricht University Medical Center, Maastricht University, PO Box 5800, 6202, Maastricht, The Netherlands. moniquemaas@live.nl.|Department of Radiology, The Netherlands Cancer Institute, Amsterdam, The Netherlands. moniquemaas@live.nl.|GROW-School for Oncology and Developmental Biology, PO Box 616, 6200, Maastricht, The Netherlands. moniquemaas@live.nl.
authors.forename: Monique
authors.initials: M
authors.lastname: Maas
authors.affiliation: Department of Radiology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.|GROW-School for Oncology and Developmental Biology, PO Box 616, 6200, Maastricht, The Netherlands.
authors.forename: Regina G
authors.initials: RG
authors.lastname: Beets-Tan
authors.affiliation: Department of Radiology, Maastricht University Medical Center, Maastricht University, PO Box 5800, 6202, Maastricht, The Netherlands.
authors.forename: Myrthe
authors.initials: M
authors.lastname: Berkhof
authors.affiliation: GROW-School for Oncology and Developmental Biology, PO Box 616, 6200, Maastricht, The Netherlands.
authors.forename: Doenja M
authors.initials: DM
authors.lastname: Lambregts
authors.affiliation: Department of Epidemiology, Maastricht University Medical Center, Maastricht University, PO Box 5800, 6202 AZ, Maastricht, The Netherlands.
authors.forename: Patty J
authors.initials: PJ
authors.lastname: Nelemans
authors.affiliation: Department of Pathology, Zuyderland Medical Centre, PO Box 5500, 6130 MB, Sittard, The Netherlands.
authors.forename: Robert
authors.initials: R
authors.lastname: Riedl
authors.affiliation: GROW-School for Oncology and Developmental Biology, PO Box 616, 6200, Maastricht, The Netherlands.|Department of Surgery, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Geerard L
authors.initials: GL
authors.lastname: Beets
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D059248:Chemoradiotherapy; D005260:Female; D006801:Humans; D008198:Lymph Nodes / Q000473:pathology*; D008207:Lymphatic Metastasis / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D012004:Rectal Neoplasms / Q000473:pathology* / Q000628:therapy*
keywords: Chemoradiation; Histopathology; Nodal staging; Rectal cancer; Response