title: Age-specific changes in intrinsic breast cancer subtypes: a focus on older women.
abstract: OBJECTIVE
  Breast cancer (BC) is a disease of aging and the number of older BC patients in the U.S. is rising. Immunohistochemical data show that with increasing age, the incidence of hormone receptor-positive tumors increases, whereas the incidence of triple-negative tumors decreases. Few data exist on the frequency of molecular subtypes in older women. Here, we characterize the incidence and outcomes of BC patients by molecular subtypes and age.
  
  
  METHODS
  Data from 3,947 patients were pooled from publicly available clinical and gene expression microarray data sets. The PAM50 algorithm was used to classify tumors into five BC intrinsic subtypes: luminal A, luminal B, HER2-enriched, basal-like, and normal-like. The association of age and subtype with recurrence-free survival (RFS), overall survival, and disease-specific survival (DSS) was assessed.
  
  
  RESULTS
  The incidence of luminal (A, B, and A+B) tumors increased with age (p < .01, p < .0001, and p < .0001, respectively), whereas the percentage of basal-like tumors decreased (p < .0001). Among patients 70 years and older, luminal B, HER2-enriched, and basal-like tumors were found at a frequency of 32%, 11%, and 9%, respectively. In older women, luminal subtypes had better outcomes than basal-like and HER2-enriched subtypes. After controlling for subtype, treatment, tumor size, nodal status, and grade, increasing age had no impact on RFS or DSS.
  
  
  CONCLUSIONS
  More favorable BC subtypes increase with age, but older patients still have a substantial percentage of high-risk tumor subtypes. After accounting for tumor subtypes, age at diagnosis is not an independent prognostic factor for outcome.
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Emily O
authors.initials: EO
authors.lastname: Jenkins
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Allison M
authors.initials: AM
authors.lastname: Deal
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Carey K
authors.initials: CK
authors.lastname: Anders
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Aleix
authors.initials: A
authors.lastname: Prat
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Charles M
authors.initials: CM
authors.lastname: Perou
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Carey
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina, USA muss@med.unc.edu.
authors.forename: Hyman B
authors.initials: HB
authors.lastname: Muss
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000145:classification* / Q000175:diagnosis / Q000628:therapy; D005260:Female; D020869:Gene Expression Profiling / Q000379:methods; D006801:Humans; D008875:Middle Aged; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis; D011960:Receptors, Estrogen / Q000032:analysis; D016896:Treatment Outcome; D064726:Triple Negative Breast Neoplasms / Q000145:classification / Q000175:diagnosis / Q000628:therapy; D055815:Young Adult
chemical_list: D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; C508053:ERBB2 protein, human
keywords: Age; Breast cancer; Elderly; Gene microarray