Vol. 19, No. 2 Printed in Great Britain

International Journal of Epidemiology ©International Epidemiological Association 1990

Oral Contraceptives and Breast Cancer Risk: A Case-Control Study RANDALL E HARRIS*, EDITH A ZANG AND ERNST L WYNDER

Center in New York City between June 1979, and February 1981.9 Personal interviews were conducted by trained medical specialists at the time of hospital admission to obtain detailed information on potential breast cancer risk factors. All cases were confirmed to have primary breast cancer based upon review of the medical records and pathology reports. Controls were individually matched to the cases by age, month of diagnosis, and hospital of interview utilizing variable ratio matching: 283 cases were matched 1:1 and 118 cases were matched 2:1. Controls (as well as cases) with conditions which have been found related to birth-control pill use (primary neoplasms of the genital tract and liver, and vascular diseases) were excluded from the study. The control group had the following frequency distribution of medical conditions: 24% gastrointestinal cancers (excluding liver), 12% leukaemias or lymphomas, 12% skin cancers, 13% respiratory tract cancers, 7% sarcomas, 4% urinary tract cancers, 16% benign neoplasms (excluding benign breast lesions), 9% infectious diseases and non-malignant chronic diseases, 2% traumatic injuries, and 1% central nervous system lesions.

The issue of oral contraceptive use as a risk factor in breast cancer has been dramatically reopened via highly publicized reports showing a positive association. While earlier studies of women with relatively short exposure times had indicated no effect,M these recent retrospective investigations appear to show an elevated risk for breast cancer associated with longterm use of oral contraceptives, particularly in women who used birth control pills early in life or before their first pregnancy.5"8 In the current investigation we also focus upon breast cancer risk and the use of oral contraceptives. The study design is a case-control investigation comparing oral contraceptive use in newly diagnosed breast cancer patients to that of age-matched hospital controls with admitting diagnoses thought to be unrelated to oral contraceptive use. MATERIAL AND METHODS In this study, 401 newly diagnosed breast cancer patients and 519 suitable controls were ascertained for interview from Memorial Sloan-Kettering Cancer

Detailed risk factor data were documented at interview including demographic information, history of all pregnancies, age at first menses, age at menopause, and information on familial history of breast cancer among close relatives (viz. mother, sisters, daughters, grandmothers, and aunts). The information on oral

Division of Epidemiology, American Health Foundation, 320 East 43rd Street, New York, NY 10017, USA. 'Present address: Department of Preventive Medicine, Room B, Ohio State University, Starling-Loving Hall. 320 West Tenth Avenue, Columbus, Ohio, 43210, USA.

240

Downloaded from http://ije.oxfordjournals.org/ at University of California, San Diego on June 4, 2015

Harris RE (Division of Epidemiology, American Health Foundation, 320 East 43rd Street, New York, NY, 10017, USA), Zang E A and Wynder E L Oral contraceptives and breast cancer risk: A case-control study. IntemationalJournal of Epidemiology, 1990. 19: 240-246. The association between breast cancer risk and oral contraceptive use was examined in 401 breast cancer patients and 519 hospital controls interviewed in New York City during 1979-1981. Control subjects were ascertained utilizing variable ratio matching to the cases (2:1 or 1:1) by sex, age, hospital, and time of diagnosis. No evidence of a positive association was found between cancer risk and the duration of use in either parous or nulliparous women. The odds ratios obtained by comparing users to non-users in women under 50 years of age after adjusting for other risk factors were 0.8 (95% Cl - 0.4-1.4) for less than five years duration and 0.4 (95% Cl - 0.2-0.8) for five or more years duration (P

Oral contraceptives and breast cancer risk: a case-control study.

The association between breast cancer risk and oral contraceptive use was examined in 401 breast cancer patients and 519 hospital controls interviewed...
380KB Sizes 0 Downloads 0 Views