Prospective study of estrogen replacement therapy and risk of breast cancer in postmenopausal women.
We prospectively examined the use of estrogen replacement therapy in relation to breast cancer incidence in a cohort of women 30 to 55 years of age in 1976. During 367 187 person-years of follow-up among postmenopausal women, 722 incident cases of breast cancer were documented. Overall, past users of replacement estrogen were not at increased risk (relative risk, 0.98; 95% confidence interval, 0.81 to 1.18), including even those with more than 10 years since last [corrected] use (relative risk after adjustment for established risk factors, 0.70; 95% confidence interval, 0.45 to 1.10). However, the risk of breast cancer was significantly elevated among current users (relative risk, 1.36; 95% confidence interval, 1.11 to 1.67). Among current users, a stronger relationship was observed with increasing age but not with increasing duration of use. These data suggest that long-term past use of estrogen replacement therapy is not related to risk of breast cancer but that current use may modestly increase risk.
Colditz
G A
GA
Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115-5899.
Stampfer
M J
MJ
Willett
W C
WC
Hennekens
C H
CH
Rosner
B
B
Speizer
F E
FE
D000328:Adult; D001943:Breast Neoplasms / Q000209:etiology*; D015331:Cohort Studies; D015914:Estrogen Replacement Therapy / Q000009:adverse effects*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008593:Menopause; D008875:Middle Aged; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors