title: Predicting retroperitoneal histology in postchemotherapy testicular germ cell cancer: a model update and multicentre validation with more than 1000 patients.
abstract: OBJECTIVE
  Surgical resection of postchemotherapy retroperitoneal lymph nodes is often performed in patients with advanced nonseminomatous testicular germ cell cancer. We previously developed a model to predict the probability that the lymph nodes contain only necrotic or fibrotic (benign) tissue versus mature teratoma and viable cancer (tumour) to identify patients who actually need resection. The present study used an updated model with new patient data and studied the validity of the updated model across various settings.
  
  
  METHODS
  We combined data of 544 patients from the original model with data of 550 new patients and performed a new logistic regression analysis, which included the same six predictors: histology of the primary tumour, prechemotherapy serum levels of alpha-fetoprotein, human chorionic gonadotropin, lactate dehydrogenase, residual mass size measured on computed tomography, and change in mass size. The validity of the updated model was studied in individual centres. Calibration of the predicted probabilities was assessed graphically and with the Hosmer-Lemeshow test. Discrimination was studied with the concordance (c)-statistic.
  
  
  RESULTS
  The updated model had slightly different, although more precise, regression coefficients. Statistically nonsignificant Hosmer-Lemeshow tests confirmed good calibration in most centres. The c-statistic for all centres except one exceeded 0.80. The updated model was valid over the complete range of predicted probabilities across a broad spectrum of centres.
  
  
  CONCLUSIONS
  This finding gives confidence in the applicability of the model to select patients for resection, particularly patients with small residual masses and low predicted probabilities of benign tissue (i.e., substantial predicted risks of residual tumour).
authors.affiliation: Center for Medical Decision Making, Department of Public Health, Erasmus MC, Rotterdam, The Netherlands. y.vergouwe@umcutrecht.nl <y.vergouwe@umcutrecht.nl>
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Vergouwe
authors.forename: Ewout W
authors.initials: EW
authors.lastname: Steyerberg
authors.forename: Richard S
authors.initials: RS
authors.lastname: Foster
authors.forename: Dirk T
authors.initials: DT
authors.lastname: Sleijfer
authors.forename: Sophie D
authors.initials: SD
authors.lastname: Fosså
authors.forename: Arthur
authors.initials: A
authors.lastname: Gerl
authors.forename: Ronald
authors.initials: R
authors.lastname: de Wit
authors.forename: J Trevor
authors.initials: JT
authors.lastname: Roberts
authors.forename: J Dik F
authors.initials: JD
authors.lastname: Habbema
mesh_terms: D006801:Humans; D008207:Lymphatic Metastasis; D008297:Male; D015233:Models, Statistical; D009373:Neoplasms, Germ Cell and Embryonal / Q000188:drug therapy* / Q000556:secondary*; D011237:Predictive Value of Tests; D012187:Retroperitoneal Space; D013736:Testicular Neoplasms / Q000188:drug therapy* / Q000473:pathology*