title: Carcinoids of unknown origin: comparative analysis with foregut, midgut, and hindgut carcinoids.
abstract: BACKGROUND
  Carcinoids are rare neuroendocrine tumors typically arising in the gastrointestinal tract. A significant percentage of these tumors present as metastatic disease of unknown primary site. The aim of this study was to better define the functional and clinical characteristics of carcinoids of unknown primary (CUP) site.
  
  
  METHODS
  This study examines the hormonal activity, clinical characteristics, and survival of 434 patients with carcinoids originating in the foregut, midgut, hindgut, or unknown location. The 143 patients with CUP were compared with the other groups with regard to presenting characteristics, diagnostic tests and therapeutic modalities used, hormonal activity, and survival.
  
  
  RESULTS
  The hormone levels (urinary 5-hydroxyindoleacetic acid and serotonin, serum and platelet serotonin) of CUP were not significantly different from midgut carcinoids with metastatic disease. Although survival with CUP was shorter than with carcinoids with identified primaries (10-year survivals of 22% vs 62%, 50%, and 48% for foregut, midgut, and hindgut, respectively), the survival curve for CUP was quite similar to that of patients with midgut carcinoids with distant disease (10-year survival of 22% vs 28%).
  
  
  CONCLUSIONS
  CUP are similar to midgut carcinoids presenting with metastatic disease with regard to hormone production and survival. Like other carcinoids, CUP can be an indolent disease process with gradual progression over decades.
authors.affiliation: Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: P M
authors.initials: PM
authors.lastname: Kirshbom
authors.forename: A R
authors.initials: AR
authors.lastname: Kherani
authors.forename: M W
authors.initials: MW
authors.lastname: Onaitis
authors.forename: J M
authors.initials: JM
authors.lastname: Feldman
authors.forename: D S
authors.initials: DS
authors.lastname: Tyler
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002276:Carcinoid Tumor / Q000175:diagnosis / Q000453:epidemiology / Q000628:therapy; D005260:Female; D006801:Humans; D007414:Intestinal Neoplasms / Q000175:diagnosis / Q000453:epidemiology / Q000628:therapy; D008297:Male; D008875:Middle Aged; D009382:Neoplasms, Unknown Primary; D013274:Stomach Neoplasms / Q000175:diagnosis / Q000453:epidemiology / Q000628:therapy; D015996:Survival Rate