Oral contraceptive and breast cancer: a case-control study

Objective To investigate the association between breast cancer and the dura tion of use of oral contraceptives (OC), and age it started to be used in a population of Pelotas, Southern Brazil. Methods There were identified 250 incident cases of breast cancer in patien ts aged 20 to 60 years from records of pathology laboratories and there wer e enrolled 1,020 controls drawn from hospital and neighbourhood population. For 90 cases identified in Pelotas. 270 hospital controls and 270 neighbou rhood controls were selected, for another 78 cases in Pelotas, 234 controls were selected. and for 82 cases from other municipalities. 246 hospital co ntrols were selected. Control were matched by age. Adjusted analysis was pe rformed using conditional logistic regression. Results No association between oral contracaptive use and breast cancer was found (OR = 1.1;CI95% 0.7-1.6 for hospital controls, and OR = 0.9:CI95% 0. 6-1.6 for neighbourhood controls) neither for different duration of use or starting age. To increase the test power, 250 cases and all 1020 controls w ere analyzed together, and an odds ratio of 1.6 (CI95% 1.0-2.4) was found f or women older than 45 years of age who had been using oral contraceptives for five years or more. Conclusions No evidence was found of a general association between oral con traceptive use and breast cancer. When analyzing the whole date set with al l neighbourhood and hospital controls together for women older than 45 year s of age who had been using oral contraceptives for more than 5 years, it w as found an increased risk almost statistically significance (p=0.05).