title: Association of the Timing of Pregnancy With Survival in Women With Breast Cancer.
abstract: OBJECTIVE
  Increasing numbers of women experience pregnancy around the time of, or after, a diagnosis of breast cancer. Understanding the effect of pregnancy on survival in women with breast cancer will help in the counseling and treatment of these women.
  
  
  OBJECTIVE
  To compare the overall survival of women diagnosed with breast cancer during pregnancy or in the postpartum period with that of women who had breast cancer but did not become pregnant.
  
  
  METHODS
  This population-based, retrospective cohort study linked health administrative databases in Ontario, Canada, comprising 7553 women aged 20 to 45 years at the time of diagnosis with invasive breast cancer, from January 1, 2003, to December 31, 2014.
  
  
  METHODS
  Any pregnancy in the period from 5 years before, until 5 years after, the index date of the diagnosis of breast cancer. Women were classified into the following 4 exposure groups: no pregnancy (the referent), pregnancy before breast cancer, pregnancy-associated breast cancer, and pregnancy following breast cancer.
  
  
  METHODS
  Five-year actuarial survival rates for all exposure groups, age-adjusted and multivariable hazard ratios [HRs] of pregnancy for overall survival for all exposure groups, and time-dependent hazard ratios for women with pregnancy following breast cancer.
  
  
  RESULTS
  Among the 7553 women in the study (mean age at diagnosis, 39.1 years; median, 40 years; range, 20-44 years) the 5-year actuarial survival rate was 87.5% (95% CI, 86.5%-88.4%) for women with no pregnancy, 85.3% (95% CI, 82.8%-87.8%) for women with pregnancy before breast cancer (age-adjusted hazard ratio, 1.03; 95% CI, 0.85-1.27; P = .73), and 82.1% (95% CI, 78.3%-85.9%) for women with pregnancy-associated breast cancer (age-adjusted hazard ratio, 1.18; 95% CI, 0.91-1.53; P = .20). The 5-year actuarial survival rate was 96.7% (95% CI, 94.1%-99.3%) for women who had pregnancy 6 months or more after diagnosis of breast cancer, vs 87.5% (95% CI, 86.5%-88.4%) for women with no pregnancy) (age-adjusted HR, 0.22; 95% CI, 0.10-0.49; P < .001).
  
  
  CONCLUSIONS
  Pregnancy did not adversely affect survival in women with breast cancer. For breast cancer survivors who wish to conceive, the risk of death is lowest if pregnancy occurs 6 months or more after diagnosis.
authors.affiliation: Women's College Research Institute, Women's College Hospital, Breast Cancer Research, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Javaid
authors.initials: J
authors.lastname: Iqbal
authors.affiliation: Institute of Health Policy, Management and Evaluation, Department of Medicine, University of Toronto, Toronto, Ontario, Canada3Cancer Clinical Research Unit, Princess Margaret Hospital, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Eitan
authors.initials: E
authors.lastname: Amir
authors.affiliation: Women's College Research Institute, Women's College Hospital, Breast Cancer Research, University of Toronto, Toronto, Ontario, Canada2Institute of Health Policy, Management and Evaluation, Department of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Paula A
authors.initials: PA
authors.lastname: Rochon
authors.affiliation: Women's College Research Institute, Women's College Hospital, Breast Cancer Research, University of Toronto, Toronto, Ontario, Canada4Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada.
authors.forename: Vasily
authors.initials: V
authors.lastname: Giannakeas
authors.affiliation: Women's College Research Institute, Women's College Hospital, Breast Cancer Research, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Ping
authors.initials: P
authors.lastname: Sun
authors.affiliation: Women's College Research Institute, Women's College Hospital, Breast Cancer Research, University of Toronto, Toronto, Ontario, Canada5Dalla Lana School of Public Health, Department of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Narod
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000401:mortality* / Q000473:pathology / Q000628:therapy; D016208:Databases, Factual; D005260:Female; D006801:Humans; D009864:Ontario / Q000453:epidemiology; D049590:Postpartum Period; D011247:Pregnancy; D011252:Pregnancy Complications, Neoplastic / Q000401:mortality* / Q000473:pathology / Q000628:therapy; D011379:Prognosis; D016016:Proportional Hazards Models; D012042:Registries; D012189:Retrospective Studies; D016019:Survival Analysis; D055815:Young Adult