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OCS AND BREAST CANCER: CDC/NIH STUDY CONTRADICTS PREVIOUS INVESTIGATIONS

Executive Summary

OCS AND BREAST CANCER: CDC/NIH STUDY CONTRADICTS PREVIOUS INVESTIGATIONS that found a link between oral contraceptive use and breast cancer. In the Nov. 2 issue of Lancet, Bruce Stadel, MD, et al, report the results of an analysis of data from the Cancer and Steroid Hormone Study which found "there was no significant increase or decrease in the risk of breast cancer for OC users according to age at first use or subsequent duration of use, even for women who first used OCs before the age of 20 years and who continued to use them for more than four years." The Cancer and Steroid Hormone Study, a population-based, case-control investigation of OC use and the risk of cancer of the breast, endometrium, and ovary in women 20-54 years of age, was conducted by the Centers for Disease Control and the Natl. Institute of Child Health and Human Development (NICHD). The analysis of breast cancer involved a comparison of 2,088 women diagnosed with breast cancer between December 1980 and December 1982 and 2,065 controls selected during the same period. The study also examined whether there was an association between pill use and the age of breast cancer diagnosis, pill use before first pregnancy, and the use of pills with high progestagen potency. Stadel, et al, reported: "Risk was not altered significantly for women who used OCs with high progestagen 'potency' before the age of 25 years (even when duration of use exceeded six years), for those who used OCs before first-term pregnancy (even when duration of use exceeded four years), or for OC users according to age at diagnosis." Two earlier studies published in 1983 -- the Pike and McPherson studies -- suggested use of OCs by young women increased their risk of breast cancer before 45 years of age. Pike, et al, "reported that women who used OCs with high progestagen 'potency' for more than four years before age 25 were over four times more likely to have breast cancer before age 37 than women who did not use these contraceptives before age 25," the CDC/NIH investigators stated. While McPherson, et al, "described preliminary data from an ongoing study which suggested that women who used OCs (regardless of potency) for longer than four years before their first term-pregnancy might be about three times more likely to have breast cancer before 45 than women who did not use OCs before first term-pregnancy." An editorial in the same issue of Lancet, while noting that the CDC/NIH study "presents strong epidemiological evidence" that early OC use is not associated with any change in risk of breast cancer, cautions that "there is a danger of accepting comfortable results on OCs and breast cancer before we can be certain that there is no effect." Noting that other epidemiological studies have had different results, the editorial says that "as long ago as 1981 the cohort study of the Royal College of General Practitioners indicated that among women under 35 years old at diagnosis there was a threefold increased risk of breast cancer, of borderline statistical significance, associated with ever-use of the pill." The editorial adds that "of the two large British cohort studies this was the only one to recruit very young women at some risk of long-term exposure before their first pregnancy. The editorial states: "If there is a latent period, then the overall results of all epidemiological studies that include young cases of breast cancer will underestimate any real effect of the long-term risk of early use of the pill, if there is one. If one assumes, for the sake of illustration, that four years or more of OC use before age 25 multiplies the risk of detectable breast cancer by three -- but only after 10 years -- then certain breast cancer incidence characteristics follow." The CDC/NIH investigators published their evaluation of the association between OC use and endometrial and ovarian cancer two years ago. They found that OC use for a year or more was associated with a 50% reduction in risk of developing cancer of the uterus and that women who had used OCs for as little as three months also had a 50% lower risk of developing ovarian cancer than women who had not used OCs. At a press conference highlighting publication of the recent CDC/NIH analysis, NICHD Contraceptive Evaluation Branch Chief Jeffrey Perlman, MD, noted that the investigators are launching a study to determine whether there is an increased risk of cervical cancer in women who use the pill. He said the study will probably be completed in three years. Stadel commented that cervical cancer "appears strongly to be a sexually reansmitted disease," but that there are "grounds for concern" that OCs may increase the progression rate of dysplasia in cervical cancer.
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