Case-Control Study On The Association Of Induced Abortion With The Risk Of Breast Cancer

[BACKGROUND] Previous studies on the relationship between induced abortion and the risk of breast cancer were contradicted, which may be due to the underreporting of abortion in controls and recall bias. Induced abortion is a legal and common procedure to terminate unwanted pregnancy in China. Women who have induced abortions would not feel stigmatized.[PURPOSE] The purpose of the study is to explore the association between Induced abortion and the risk of breast cancer and whether the detailed characteristics of the abortion affect the association.[METHODS] A population-based case-control study, which was conducted between 1998 and 2001 in urban Shanghai, was carried out to assess the relationship between a history of induced abortion and risk of breast cancer. A total of 1,495 cases of breast cancer and 1,573 age-frequently-matched controls were interviewed individually, with response rates of 95.1% and 87.7% respectively. Subjects' demographic characteristics and potential risk factors of breast cancer were collected. Among them, 52 cases and 61 controls refused to be interviewed. Data from Shanghai family planning registry system were used to check the history of induced abortion reported by cases and controls.[RESULTS] Only 133 participants (3.4%) were nulliparous in this study. Therefore, we focus this analysys among the parous subjects. After adjusting for potential confounders, induced abortions were not found to be associated with breast cancer (odds ratio [OR]=0.94, 95% confidence interval [CI] = 0.79-1.11). Moreover, the relationship between induced abortion and breast cancer was different among postmenopausal women (OR=0.57, 95%CI=0.36 -0.90) and among premenopausal ones (OR=1.03,95%CI=0.85-1.25). Women with longer gestational age at abortion were less likely to have breast caner than their counterparts. No risks were found to be associated with the specific characteristics of induced abortion, such as age at the first abortion, the timing of the first induced abortion (before or after the first live birth), symptoms due to pregnancy, medicines taken during conception, places where pregnancy was terminated, and reasons for induced abortionSpontaneous abortion was not found to be associated with breast cancer risk in this study. Neither the number of spontaneous abortion nor the age at first spontaneous abortion and the timing of the first spontaneous abortion (before or after the first live birth) was found to be related with the risk of breast cancer.It was found in this study that many factors other than induced abortion were associated with the risk of breast cancer, which included educational level, occupation, age at menarche, menopause status, the numbers of pregnancies, the numbers of births, hormone medicine taken, family history of breast cancer, benign breast diseases, tea drinking, physical activities, as well as daily food (such as eggs,milk, legume, fresh vegetables, fresh fruits, meat, seafood and preserved food).[CONCLUSIONS] The results suggest that a history of induced abortions does not increase the risk of breast cancer among Chinese women. Moreover, It declines this risk among postmenopausal ones. No association was found between spontaneous abortion and risk of breast cancer.