title: Metastatic breast cancer in young women: a population-based cohort study to describe risk and prognosis.
abstract: BACKGROUND
  There is limited information on the risk of metastatic breast cancer (MBC) to inform younger women, particularly those under 40 years.
  
  
  OBJECTIVE
  We conducted a retrospective analysis of a population-based cohort study to describe the risk, site and prognosis of MBC in young women under 40 years with an initial diagnosis of non-metastatic breast cancer and compared with older women.
  
  
  METHODS
  Data were extracted from the New South Wales Central Cancer Registry and the Admitted Patient Data Collection database between 2001-2007. Main outcome measures were 5-year cumulative incidence of MBC, prognostic factors for MBC and overall survival (OS) from the date of MBC diagnosis.
  
  
  RESULTS
  Three hundred and ninety-five (6%) of 6640 women with non-metastatic BC were <40 years. The 5-year cumulative incidence of MBC was 24% (95% CI 20-29%) for women <40 years with non-metastatic BC, compared with 9% (95% CI 9-10%) for women ≥40 years. Significant independent risk factors for MBC ≤ 5 years were age <40, regional disease at diagnosis, low socioeconomic status and the presence of other non-breast primary. At first record of MBC, visceral sites were more common for women <40 years than ≥40 (54% vs 43%; P = 0.03). Median survival for women with MBC within 5 years was not significantly different between young and older women (<40 years 18 months vs ≥40 years 14 months; log-rank P = 0.21).
  
  
  CONCLUSIONS
  Women with non-metastatic BC before age 40 have a higher 5-year risk of developing MBC than older women. There were no significant differences in median survival following MBC between young and older women.
authors.affiliation: NHMRC Clinical Trials Centre, University of Sydney, Sydney, New South Wales, Australia; School of Public Health, Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Tjokrowidjaja
authors.forename: C K
authors.initials: CK
authors.lastname: Lee
authors.forename: N
authors.initials: N
authors.lastname: Houssami
authors.forename: S
authors.initials: S
authors.lastname: Lord
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000556:secondary*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D009362:Neoplasm Metastasis; D009517:New South Wales / Q000453:epidemiology; D011159:Population Surveillance; D011379:Prognosis; D012189:Retrospective Studies; D012307:Risk Factors; D015996:Survival Rate / Q000639:trends; D055815:Young Adult
keywords: breast neoplasms; epidemiologic research design; neoplasm metastasis; population characteristics; prognosis