title: The occurrence of rare cancers in U.S. adults, 1995-2004.
abstract: OBJECTIVE
  Rare cancers have been traditionally understudied, reducing the progress of research and hindering decisions for patients, physicians, and policy makers. We evaluated the descriptive epidemiology of rare cancers using a large, representative, population-based dataset from cancer registries in the United States.
  
  
  METHODS
  We analyzed more than 9 million adult cancers diagnosed from 1995 to 2004 in 39 states and two metropolitan areas using the Cancer in North America (CINA) dataset, which covers approximately 80% of the U.S. population. We applied an accepted cancer classification scheme and a published definition of rare (i.e., fewer than 15 cases per 100,000 per year). We calculated age-adjusted incidence rates and rare/non-rare incidence rate ratios using SEER*Stat software, with analyses stratified by gender, age, race/ethnicity, and histology.
  
  
  RESULTS
  Sixty of 71 cancer types were rare, accounting for 25% of all adult tumors. Rare cancers occurred with greater relative frequency among those who were younger, nonwhite, and of Hispanic ethnicity than among their older, white, or non-Hispanic counterparts.
  
  
  CONCLUSIONS
  Collectively, rare tumors account for a sizable portion of adult cancers, and disproportionately affect some demographic groups. Maturing population-based cancer surveillance data can be an important source for research on rare cancers, potentially leading to a greater understanding of these cancers and eventually to improved treatment, control, and prevention.
authors.affiliation: Epidemiology Research Center, Marshfield Clinic Research Foundation, 1000 North Oak Ave., MS ML2, Marshfield, WI 54449, USA. greenlee.robert@mcrf.mfldclin.edu
authors.forename: Robert T
authors.initials: RT
authors.lastname: Greenlee
authors.forename: Marc T
authors.initials: MT
authors.lastname: Goodman
authors.forename: Charles F
authors.initials: CF
authors.lastname: Lynch
authors.forename: Charles E
authors.initials: CE
authors.lastname: Platz
authors.forename: Lori A
authors.initials: LA
authors.lastname: Havener
authors.forename: Holly L
authors.initials: HL
authors.lastname: Howe
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D016208:Databases, Factual; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000145:classification / Q000453:epidemiology* / Q000208:ethnology; D035583:Rare Diseases / Q000453:epidemiology*; D018426:SEER Program; D014481:United States / Q000453:epidemiology; D055815:Young Adult
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