title: Occurrence of breast cancer subtypes in adolescent and young adult women.
abstract: BACKGROUND
  Breast cancers are increasingly recognized as heterogeneous based on expression of receptors for estrogen (ER), progesterone (PR), and human epidermal growth factor receptor 2 (HER2). Triple-negative tumors (ER-/PR-/HER2-) have been reported to be more common among younger women, but occurrence of the spectrum of breast cancer subtypes in adolescent and young adult (AYA) women aged between 15 and 39 years is otherwise poorly understood.
  
  
  METHODS
  Data regarding all 5,605 AYA breast cancers diagnosed in California during the period 2005 to 2009, including ER and PR status (referred to jointly as hormone receptor (HR) status) and HER2 status, was obtained from the population-based California Cancer Registry. Incidence rates were calculated by subtype (triple-negative; HR+/HER2-; HR+/HER2+; HR-/HER2+), and logistic regression was used to evaluate differences in subtype characteristics by age group.
  
  
  RESULTS
  AYAs had higher proportions of HR+/HER2+, triple-negative and HR-/HER2+ breast cancer subtypes and higher proportions of patients of non-White race/ethnicity than did older women. AYAs also were more likely to be diagnosed with stage III/IV disease and high-grade tumors than were older women. Rates of HR+/HER2- and triple-negative subtypes in AYAs varied substantially by race/ethnicity.
  
  
  CONCLUSIONS
  The distribution of breast cancer subtypes among AYAs varies from that observed in older women, and varies further by race/ethnicity. Observed subtype distributions may explain the poorer breast cancer survival previously observed among AYAs.
authors.affiliation: Cancer Prevention Institute of California, 2201 Walnut Ave, Suite 300, Fremont, CA 94538, USA. theresa.keegan@cpic.org
authors.forename: Theresa H M
authors.initials: TH
authors.lastname: Keegan
authors.forename: Mindy C
authors.initials: MC
authors.lastname: DeRouen
authors.forename: David J
authors.initials: DJ
authors.lastname: Press
authors.forename: Allison W
authors.initials: AW
authors.lastname: Kurian
authors.forename: Christina A
authors.initials: CA
authors.lastname: Clarke
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000378:metabolism*; D002140:California; D005260:Female; D006801:Humans; D008875:Middle Aged; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism*; D011980:Receptors, Progesterone / Q000378:metabolism*; D055815:Young Adult
chemical_list: D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; C508053:ERBB2 protein, human