Oral contraceptives and breast cancer: a case-control study with hospital and community controls

Article Abstract:

Several recent research studies have found an increased risk of breast cancer in women who have used oral contraceptives (OC, birth control pills), but this relationship has been questioned by other studies. In order to resolve the inconsistency, a case-control study was carried out with 158 breast cancer patients who met certain criteria (the 'cases'). Characteristics of these patients were compared with those of a control group of women (326 hospital controls) admitted to the same hospitals as the cases at approximately the same time, and with those of a group of 1,140 women living in the nearby community. Detailed information regarding menstrual and reproductive histories, medical problems, past surgeries, and related topics was obtained by interview and questionnaire. All subjects were also questioned regarding their use of hormone supplements and OCs. No difference was found in OC use among the groups; 42 percent of both the case and hospital control groups had used them, as had 48 percent of the community controls. However, women who had never given birth to a child and who had used OCs for five years or more were at greater risk of developing breast cancer than women in either control group. It should be noted that the numbers of women in this particular comparison were small, so the results may not be representative of the population as a whole. No such relationship was found for women who had children. Also, an unexpected elevated risk for breast cancer was found for premenopausal women in the 45- to 59-year-old age group; risk increased with longer duration of OC use. A discussion is provided regarding the limits of the study, which should be considered when interpreting these results. In general, the results are presented as reassuring for young women who use OCs in that there was little association between breast cancer and OC use. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Age-specific differences in the relationship between oral contraceptive use and breast cancer

Article Abstract:

Most studies have shown that the use of oral contraceptives among women between the ages of 20 to 54 years does not increase the risk of breast cancer. However, some studies have shown an increased risk for breast cancer among oral contraceptive users aged 35 years or less. Marital status, age at the start of menstruation, age at first completed pregnancy, race, and birth place are other factors that influence the risk of developing breast cancer. The risk of breast cancer is increased among women less than 35 years who have a high parity (more pregnancies) compared with women of the same age with low parity. However, high parity is associated with a reduced risk of breast cancer after ages 35 to 40. It is possible that the association between breast cancer and oral contraceptive use may also vary with age. The Cancer and Steroid Hormone Study examined the relationship between oral contraceptive use and the risk of breast cancer. The study was conducted in eight regions of the US between 1980 and 1982. Re-analysis of these data suggested that the relationship between oral contraceptive use and risk of breast cancer varied with age. The risk of breast cancer was slightly increased among oral contraceptive users aged 20 to 34 years, but was slightly decreased among women aged 45 to 54 years. No relationship was found between oral contraceptive use and risk of breast cancer among women aged 35 to 44 years. A reduction in the risk of breast cancer among oral contraceptive users aged 45 to 54 years was enhanced by increasing duration of oral contraceptive use. These findings should not alter the current prescribing practices or use of oral contraceptives. (Consumer Summary produced by Reliance Medical Information, Inc.)

Evaluation, Age factors in disease, Disease age factors

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Oral contraception and congenital malformations in offspring: a review and meta-analysis of the prospective studies

Article Abstract:

Results from small research studies may be inconclusive because relatively few subjects are used. There is a technique called meta-analysis which allows results from many studies to be combined according to specific statistical procedures; the purpose is to reach a conclusion based upon all the studies included. The risk of birth defects from use of oral contraceptives (OC) during early pregnancy is a subject that has been widely studied, but many studies have focussed on small, carefully defined groups of women. The techniques of meta-analysis were used to evaluate 12 prospective, carefully controlled studies on this issue. A discussion is provided of the assumptions underlying study selection. The results argue strongly against an association between OC use in early pregnancy and subsequent malformations in stillborn or live-born infants. Malformations may, however, be present in fetuses that are aborted spontaneously. Overall, few women with this history of OC use actually deliver children, so risk estimates tend to vary widely. The lack of relationship between OC use in early pregnancy and birth defects according to this meta-analysis is thus similar to the conclusions of the majority of individual well-designed studies. (Consumer Summary produced by Reliance Medical Information, Inc.)

Causes of, Surveys, Birth defects, Contraception, Contraception failures, Teratogenic agents

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