title: Estrogen plus progestin and breast cancer incidence and mortality in the Women's Health Initiative Observational Study.
abstract: BACKGROUND
  In the Women's Health Initiative (WHI) randomized trial, estrogen plus progestin increased both breast cancer incidence and mortality. In contrast, most observational studies associate estrogen plus progestin with favorable prognosis breast cancers. To address differences, a cohort of WHI observational study participants with characteristics similar to the WHI clinical trial was studied.
  
  
  METHODS
  We identified 41 449 postmenopausal women with no prior hysterectomy and mammogram negative within 2 years who were either not hormone users (n = 25 328) or estrogen and progestin users (n = 16 121). Multivariable-adjusted Cox proportional hazard regression was used to calculate hazard ratios (HRs) with 95% confidence intervals (CI). All statistical tests were two-sided.
  
  
  RESULTS
  After a mean of 11.3 (SD = 3.1) years, with 2236 breast cancers, incidence was higher in estrogen plus progestin users than in nonusers (0.60% vs 0.42%, annualized rate, respectively; HR = 1.55, 95% CI = 1.41 to 1.70, P < .001). Women initiating hormone therapy closer to menopause had higher breast cancer risk with linear diminishing influence as time from menopause increased (P < .001). Survival after breast cancer, measured from diagnosis, was similar in combined hormone therapy users and nonusers (HR = 1.03, 95% CI = 0.79 to 1.35). On a population basis, there were somewhat more deaths from breast cancer, measured from cohort entry (HR = 1.32, 95% CI = 0.90 to 1.93, P = .15), and more all-cause deaths after breast cancer (HR = 1.65, 95% CI = 1.29 to 2.12, P < .001) in estrogen plus progestin users than in nonusers.
  
  
  CONCLUSIONS
  Consistent with WHI randomized trial findings, estrogen plus progestin use is associated with increased breast cancer incidence. Because prognosis after diagnosis on combined hormone therapy is similar to that of nonusers, increased breast cancer mortality can be expected.
authors.affiliation: Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA, 90502, USA. rowanchlebowski@gmail.com
authors.forename: Rowan T
authors.initials: RT
authors.lastname: Chlebowski
authors.forename: JoAnn E
authors.initials: JE
authors.lastname: Manson
authors.forename: Garnet L
authors.initials: GL
authors.lastname: Anderson
authors.forename: Jane A
authors.initials: JA
authors.lastname: Cauley
authors.forename: Aaron K
authors.initials: AK
authors.lastname: Aragaki
authors.forename: Marcia L
authors.initials: ML
authors.lastname: Stefanick
authors.forename: Dorothy S
authors.initials: DS
authors.lastname: Lane
authors.forename: Karen C
authors.initials: KC
authors.lastname: Johnson
authors.forename: Jean
authors.initials: J
authors.lastname: Wactawski-Wende
authors.forename: Chu
authors.initials: C
authors.lastname: Chen
authors.forename: Lihong
authors.initials: L
authors.lastname: Qi
authors.forename: Shagufta
authors.initials: S
authors.lastname: Yasmeen
authors.forename: Polly A
authors.initials: PA
authors.lastname: Newcomb
authors.forename: Ross L
authors.initials: RL
authors.lastname: Prentice
mesh_terms: D000368:Aged; D014408:Biomarkers, Tumor / Q000032:analysis; D001943:Breast Neoplasms / Q000139:chemically induced* / Q000737:chemistry / Q000453:epidemiology* / Q000401:mortality / Q000473:pathology; D018270:Carcinoma, Ductal, Breast / Q000139:chemically induced* / Q000737:chemistry / Q000453:epidemiology* / Q000473:pathology; D015914:Estrogen Replacement Therapy / Q000009:adverse effects* / Q000379:methods*; D004967:Estrogens / Q000008:administration & dosage / Q000009:adverse effects*; D005260:Female; D006801:Humans; D015994:Incidence; D008207:Lymphatic Metastasis; D008875:Middle Aged; D017698:Postmenopause; D011372:Progestins / Q000008:administration & dosage / Q000009:adverse effects*; D011379:Prognosis; D018426:SEER Program; D014481:United States / Q000453:epidemiology; D016387:Women's Health
chemical_list: D014408:Biomarkers, Tumor; D004967:Estrogens; D011372:Progestins
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