Previous oral contraceptive use and breast cancer risk according to hormone replacement therapy use among postmenopausal women.
OBJECTIVE
To assess postmenopausal breast cancer risk in relation to particular patterns of oral contraceptive (OC) use according to hormone replacement therapy (HRT) exposure.


METHODS
Time-dependent Cox regression models were used to analyse information on postmenopausal women from a large-scale French cohort. Among a total of 68,670 women born between 1925 and 1950, 1405 primary invasive postmenopausal breast cancer cases were identified from 1992 to 2000.


RESULTS
A non-significant decrease in risk of around 10% was associated with ever OC use as compared to never OC use in postmenopausal women. No significant interaction was found between OC and HRT use on postmenopausal breast cancer risk. Breast cancer risk decreased significantly with increasing time since first OC use (test for trend: p=0.01); this was consistent after adjustment for duration of use or for time since last use.


CONCLUSIONS
No increase in breast cancer risk was associated with previous OC exposure among postmenopausal women, probably because the induction window had closed. Some women may develop breast cancer soon after exposure to OCs, leading to a deficit of cases of older women. Further investigation is therefore required to identify young women at high risk.
Institute of Community Medicine, University of Tromsø, France.
Vanessa
V
Dumeaux
Agnès
A
Fournier
Eiliv
E
Lund
Françoise
F
Clavel-Chapelon
D000328:Adult; D001943:Breast Neoplasms / Q000453:epidemiology*; D015331:Cohort Studies; D003278:Contraceptives, Oral, Hormonal / Q000627:therapeutic use*; D005260:Female; D005500:Follow-Up Studies; D005602:France / Q000453:epidemiology; D020249:Hormone Replacement Therapy; D006801:Humans; D008875:Middle Aged; D017698:Postmenopause; D016016:Proportional Hazards Models; D018570:Risk Assessment; D011795:Surveys and Questionnaires; D013997:Time Factors
D003278:Contraceptives, Oral, Hormonal