title: Proportion and characteristics of men with unknown risk category in the National Prostate Cancer Register of Sweden.
abstract: BACKGROUND
  Knowledge on missing data in a clinical cancer register is important to assess the validity of research results. For analysis of prostate cancer (Pca), risk category, a composite variable based on serum levels of prostate specific antigen (PSA), stage, and Gleason score, is crucial for treatment decisions and a strong determinant of outcome. The aim of this study was to assess the proportion and characteristics of men in the National Prostate Cancer Register (NPCR) of Sweden with unknown risk category.
  
  
  METHODS
  Men diagnosed with Pca between 1998 and 2012 registered in NPCR with known or unknown risk category were compared with respect to age, socioeconomic factors, comorbidity, cancer characteristics, cancer treatment, and mortality from Pca and other causes.
  
  
  RESULTS
  In total, 3315 of 129 391 (3%) men had unknown risk category. Compared to other men in NPCR, these men more often had a concomitant bladder cancer diagnosis, 19% versus 1%, diagnosis of benign prostatic hyperplasia 31% versus 5%, received unspecified Pca treatment 16% versus 3%, had higher comorbidity, Charlson Comorbidity Index 2 or higher, 34% versus 13%, and had lower Pca mortality 12% versus 30%, but similar mortality from other causes.
  
  
  CONCLUSIONS
  Men with unknown risk category were rare in NPCR but distinctly different from other men in NPCR in many aspects including higher comorbidity and lower Pca mortality.
authors.affiliation: a Department of Surgical and Perioperative Sciences, Urology and Andrology , Umeå University Hospital , Umeå , Sweden.
authors.forename: Katarina
authors.initials: K
authors.lastname: Tomic
authors.affiliation: b Regional Cancer Center Uppsala Örebro, Uppsala University Hospital , Uppsala , Sweden.
authors.forename: Marcus
authors.initials: M
authors.lastname: Westerberg
authors.affiliation: a Department of Surgical and Perioperative Sciences, Urology and Andrology , Umeå University Hospital , Umeå , Sweden.|c Department of Urology , Ryhov Hospital , Jönköping , Sweden.
authors.forename: David
authors.initials: D
authors.lastname: Robinson
authors.affiliation: b Regional Cancer Center Uppsala Örebro, Uppsala University Hospital , Uppsala , Sweden.
authors.forename: Hans
authors.initials: H
authors.lastname: Garmo
authors.affiliation: a Department of Surgical and Perioperative Sciences, Urology and Andrology , Umeå University Hospital , Umeå , Sweden.|d Department of Surgical Sciences , Uppsala University , Uppsala , Sweden.
authors.forename: Pär
authors.initials: P
authors.lastname: Stattin
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D015897:Comorbidity; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D009382:Neoplasms, Unknown Primary / Q000453:epidemiology*; D011379:Prognosis; D011471:Prostatic Neoplasms / Q000175:diagnosis*; D012042:Registries; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult