The pill does not raise the risk of breast cancer, not even among women who started taking it early or have close relatives with the disease, a new study found.
Previous research had reached conflicting conclusions, though two of the most recent studies had found a higher risk for some women. And since nearly 80 percent of U.S. women born since 1945 have used oral contraceptives, even a small increase was reason for concern.
In this new study, published in Thursday's New England Journal of Medicine, scientists at the Centers for Disease Control and Prevention and the National Institutes of Health looked at more than 9,200 women ages 35 to 64, a group that includes the first generation of women to take the pill.
"It was a chance to look at women over a lifetime to see what the risk has been," said Robert Spirtas, chief of the contraception and reproductive health branch of the National Institute of Child Health and Human Development. "That hasn't been possible before, because the first oral contraceptive users started off in the 1960s. They're just getting to the age where the breast cancer risk is highest."
Researchers in Atlanta, Detroit, Los Angeles, Philadelphia and Seattle interviewed 4,575 women who had breast cancer and 4,682 who did not. Seventy-seven percent of the cancer patients and 79 percent of the cancer-free women had taken some type of oral contraceptive.
Those who had never taken the pill were about as likely to have breast cancer as those who were taking it or had taken it.
It did not matter whether they were black or white; whether they were fat, skinny or of average weight; whether they took the early variety of the pill containing high doses of hormones, or a later, lower-dose pill; or whether they had a family history of breast cancer, had gone through menopause or started taking contraceptives before they were 20.
"I think that what was impressive was that, no matter which way you looked at the data, no matter which subset, the result was null," said Dr. Kathy J. Helzlsouer, a cancer specialist in the epidemiology department at Johns Hopkins University's school of public health. "It's nice to be able to give good news to women about something so many women take or have taken."
A 1996 analysis of 54 studies had concluded that the pill does seem to raise the breast cancer risk, perhaps by about one-quarter. And a more recent study indicated that oral contraceptives can at least triple the risk in women whose relatives have had breast cancer.
Dr. Claudine Isaacs, clinical director of the breast cancer program at Georgetown University Hospital, said the latest study did not look far enough to say with certainty whether the pill raises the risk for women whose relatives have had the disease.
For one thing, women were asked only if their mother or any sister or daughter had breast or ovarian cancer, not whether it had been found in any aunts, cousins or grandmothers, Isaacs said.
"I think we still have to be a little cautious about women with a strong family history, or who we know have mutations. Studies are going to be coming out shortly about those," she said.
But, she said, the latest findings should reassure the vast majority of women.
"I think this is a definitive study," she said.