Oral contraceptives, postmenopausal hormones, and risk of asynchronous bilateral breast cancer: the WECARE Study Group.
OBJECTIVE
To investigate whether oral contraceptive (OC) use and postmenopausal hormones (PMH) are associated with an increased risk of developing asynchronous bilateral breast cancer among women diagnosed with breast cancer younger than 55 years.


METHODS
The WECARE (Women's Environment, Cancer, and Radiation Epidemiology) study is a population-based, multicenter, case-control study of 708 women with asynchronous bilateral breast cancer and 1,395 women with unilateral breast cancer. Risk factor information collected during a telephone interview focused on exposures before and after the first breast cancer diagnosis. Treatment and tumor characteristics were abstracted from medical records. Multivariable conditional logistic regression was used to estimate rate ratios (RR) and 95% CIs.


RESULTS
OC use before the first breast cancer diagnosis was not associated with risk of asynchronous bilateral breast cancer (RR = 0.88; 95% CI, 0.67 to 1.16). OC use after breast cancer diagnosis was also not significantly associated with risk (RR = 1.56; 95% CI, 0.71 to 3.45). Risk did not increase with longer duration of use or among women who had begun using OCs at a younger age. No evidence of an increased risk of asynchronous bilateral breast cancer was observed with PMH use before (RR = 1.21; 95% CI, 0.90 to 1.61) or after breast cancer diagnosis (RR = 1.10; 95% CI, 0.67 to 1.77). Neither duration nor type of PMH were associated with risk. Age at and time since first breast cancer diagnosis did not substantially affect these results.


CONCLUSIONS
This study provides no strong evidence that OC or PMH use increases the risk of a second cancer in the contralateral breast.
Figueiredo
Jane C
JC
Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
Bernstein
Leslie
L
Capanu
Marinela
M
Malone
Kathleen E
KE
Lynch
Charles F
CF
Anton-Culver
Hoda
H
Stovall
Marilyn
M
Bertelsen
Lisbeth
L
Haile
Robert W
RW
Bernstein
Jonine L
JL
D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000139:chemically induced* / Q000453:epidemiology* / Q000208:ethnology / Q000628:therapy; D016022:Case-Control Studies; D003276:Contraceptives, Oral / Q000008:administration & dosage / Q000009:adverse effects*; D003278:Contraceptives, Oral, Hormonal / Q000009:adverse effects; D003718:Denmark / Q000453:epidemiology; D005260:Female; D012739:Gonadal Steroid Hormones / Q000097:blood*; D006801:Humans; D016015:Logistic Models; D008875:Middle Aged; D015999:Multivariate Analysis; D016609:Neoplasms, Second Primary / Q000139:chemically induced* / Q000453:epidemiology* / Q000208:ethnology; D016017:Odds Ratio; D017698:Postmenopause; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology
D003276:Contraceptives, Oral; D003278:Contraceptives, Oral, Hormonal; D012739:Gonadal Steroid Hormones