Estrogen and estrogen-progestin replacement therapy and risk of postmenopausal breast cancer in Canada.
OBJECTIVE
To examine the association between hormone replacement therapy (HRT) use and breast cancer incidence and to determine whether the association differs according to type of regimen.


METHODS
Data were collected in Ontario from 404 incident cases and 403 age frequency-matched controls, between 1995 and 1996, using a self-administered questionnaire.


RESULTS
Multivariate analyses revealed an elevated odds ratio among long-term (> or = ten years) HRT users (odds ratio (OR) = 1.80, 95% confidence interval (CI) 1.06-3.06). Risk among long-term estrogen-progestin users was substantially higher (OR = 3.48, 95% CI 1.00-12.11) than risk among long-term users of estrogen alone (OR = 1.74, 95% CI 0.93-3.24). Among both estrogen and estrogen-progestin users, positive associations were not observed for durations of use less than ten years.


CONCLUSIONS
These data suggest that long-term use of HRT increases the risk of breast cancer and that estrogen-progestin therapy may be more detrimental than estrogen use alone.
Kirsh
Victoria
V
Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, CT, USA.
Kreiger
Nancy
N
D000368:Aged; D001943:Breast Neoplasms / Q000139:chemically induced* / Q000453:epidemiology; D002170:Canada / Q000453:epidemiology; D016022:Case-Control Studies; D016001:Confidence Intervals; D015914:Estrogen Replacement Therapy / Q000009:adverse effects*; D004967:Estrogens / Q000009:adverse effects*; D005260:Female; D006801:Humans; D015994:Incidence; D016013:Likelihood Functions; D008875:Middle Aged; D015999:Multivariate Analysis; D016017:Odds Ratio; D009864:Ontario / Q000453:epidemiology; D017698:Postmenopause; D011372:Progestins / Q000009:adverse effects*; D012307:Risk Factors
D004967:Estrogens; D011372:Progestins