Low-dose oral contraceptives are as protective against ovarian cancer as are older, high-dose pills, find University of Pittsburgh researchers

July 23, 2000

PITTSBURGH, July 24 -- Low-dose contraceptives currently on the market are just as effective as the older, high-dose preparations in protecting women from ovarian cancer, according to investigators from the University of Pittsburgh Graduate School of Public Health (GSPH) in a paper published in the August 1 issue of the American Journal of Epidemiology.

"Our study shows that women who are taking, or have taken, low-dose oral contraceptives have a 40 percent reduction in risk of ovarian cancer--the same risk reduction provided by the older, high-dose birth-control pills," said senior author Roberta Ness, M.D., M.P.H., associate professor of epidemiology at the University of Pittsburgh GSPH. In addition, researchers found that this protection begins soon after initiating use, and continues for at least 30 years after stopping use.

Previous research has shown that women taking the older, pre-1980 oral contraceptives were less likely to develop ovarian cancer than were women who had never used them. But over the past two decades the amounts of estrogen and progestin in oral contraceptives have steadily decreased, and new progestins have been introduced. The University of Pittsburgh study is the first population-based, case-controlled effort to examine risk protection offered by the newer preparations.

"Until now, few women taking the low-dose preparations had passed through the critical 20- to-30-year window during which the incidence of ovarian cancer rises," explained Dr. Ness. "Ours is the first study to observe a sufficiently long time interval between oral contraception cessation and the age at which women begin developing ovarian cancer."

Although formulations containing low-dose estrogen are equally as effective as are high-dose formulations in suppressing ovulation, researchers were unsure of whether they would be equally able to suppress gonadotropin levels, which are thought to elevate ovarian cancer risk. This study confirms that they are.

Results of the study, which involved more than 2,000 women, showed that the risk of ovarian cancer was reduced by an average of 40 percent for oral contraceptive users, regardless of age at initiation. Amounts of estrogens and progestins in the formulations did not affect the degree of protection. Cancer-protection began after a period of one to four years. Those women who stopped taking the pill 30 years ago were protected to the same degree as those who ceased less than 10 years ago. Body mass index, race, number of pregnancies and age at first menstruation and at menopause did not affect the risk.

Investigators interviewed 767 women ages 20 through 69 who had had epithelial ovarian cancer diagnosed within the previous six months. The subjects were drawn from 39 hospitals in Pennsylvania, southern New Jersey and Delaware. Also interviewed, as controls, were 1,367 women age 20-69, who were selected primarily through random telephone dialing within the same geographic areas as the subjects.

Interviews determined participants' contraceptive use, including type, frequency and duration of use; demographic information; menstrual onset, regularity and cessation; length and outcome of each pregnancy; and length of time breast-feeding. For oral contraceptives, interviewers obtained information on active ingredients and doses. Formulations containing 100 mcg or less of mestranol or 50 mcg or less of ethinyl estradiol were considered low-estrogen. Those with more than 100 mcg of mestranol or more than 50 mcg of ethinyl were high-estrogen. Formulations with 0.2 mg or less of norgestrel were considered low-progestin, 0.3-0.4 mg were intermediate, and 0.5 mg or more were high.

To validate dose findings, researchers compared women who began using the pill before 1972, when high-dose pills dominated the market; between 1972 and 1980, when the transition was underway from higher- to lower-dose formulations, and after 1980, when lower-dose pills predominated.

Investigators say further targeted research is necessary to evaluate the full benefit of oral contraceptives in protecting women with a high genetic risk for ovarian cancer. Also needed is an assessment of the trade-off between ovarian cancer risk reduction and the possible risk of thrombosis (blood clot) and possibly breast cancer, both of which have been linked to oral contraception use.
This research was supported by the National Cancer Institute.

University of Pittsburgh Medical Center

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