Women who used certain types of birth control pills may have a higher risk of developing breast cancer within the following year, compared to women who have never used oral contraceptives or have not used them recently, according to a new study.
However, the study found no relationship between an increased cancer risk and the use of low-dose estrogen pills, which are currently the most commonly prescribed type of birth control pills in the U.S., according to experts not involved in the study.
In the study, the researchers concluded that the potential increase in the risk for breast cancer varied, depending on the types of birth control pills that the women used. The use of high-dose estrogen pills was related to a 2.7-fold increase in breast cancer risk, and the use of moderate-dose estrogen was linked to a 1.6-fold increase. Pills containing ethynodiol diacetate were related to a 2.6-fold higher risk. Triphasic combination pills containing an average of 0.75 milligrams of norethindrone increased the risk 3.1-fold.
The investigators did not find a link between the use of low-dose estrogen birth control pills and an increased breast cancer risk.
"Our results suggest that use of contemporary oral contraceptives [birth control pills] in the past year is associated with an increased breast cancer risk relative to never or former oral contraceptive use, and that this risk may vary by oral contraceptive formulation," study author Elisabeth F. Beaber, a staff scientist in the Public Health Sciences Division of Fred Hutchinson Cancer Research Center in Seattle, Washington, said in a statement.
However she also added that the results "require confirmation and should be interpreted cautiously."
"Breast cancer is rare among young women and there are numerous established health benefits associated with oral contraceptive use that must be considered," she said.
Previous research has suggested that the increased risk related to recent oral contraceptive use declines after a woman stops taking birth control pills, she said.
In the study, researchers examined health records and oral contraceptive use in 1,102 women ages 20 to 49 years diagnosed with breast cancer and 21,952 women without breast cancer in the same age group. Unlike some other studies on the safety of contraceptive use that relied on data depending on women's self-report or recall, the new study was based on electronic pharmacy records that included the drug name, dosage and duration of medication use.
However, Dr. Holly Pederson, a staff physician at the Breast Services Department at the Cleveland Clinic, who was not involved in the study, expressed concern about the actual meaning of the data presented in the study. She noted that, of the 1,102 women in the study who had breast cancer, only 93 were on oral contraceptives for longer than six months. And only 30 of them took the types of oral contraceptives that were suggested to 'increase the risk of breast cancer by 50 percent' in the study, she said, referring to the pills with high doses of estrogen (50 micrograms), the ones containing the progestin ethynodiol dictate and triphasic pills containing a high dose of norethindrone acetate.
"Certainly no general conclusions can be drawn from these data and these small numbers, and these types of pills are not commonly used at the present time," Pederson told CBS News. "And, in fact, low dose monophasic pills, which are the most commonly used type of pill in this country, were not associated with increased risk."
Pederson also stressed that, even though breast cancer is the most common type of cancer in women, it is important to remember that the overall "risk of a woman developing breast cancer prior to the age of 50 is less than 2 percent."
"This [the study] is a complicated analysis of a complicated problem," Dr. Freya Schnabel, the director of breast surgery at NYU Langone Medical Center, who was not involved in the study, told CBS News.
Considering a variety of factors such as a woman's age and health background should be part of the conversation about what contraceptive pill to use at what age, Schnabel said.
Interestingly, another study called CARE (Women's Contraceptive and Reproductive Experiences), published in 2002 in the New England Journal of Medicine, found no link between the use of birth control pills and increased breast cancer risk, Pederson said. In the 2002 study, researchers compared 4,575 women with breast cancer with 4,682 women without breast cancer, ages 35 to 64, "according to age, race, presence or absence of a family history of breast cancer, and other factors," she said, adding that the researchers did not find a breast cancer risk increase in women who took birth control pills with different doses of estrogen and types of progestins, even for long periods of time. It also did not matter whether a woman started taking pills at a young age or had a history of breast cancer, and the study results were similar in white and black women, Pederson said.
So, are most birth control pills that are currently prescribed generally safe for an average woman's health?
"The low-dose monophasic pills are probably very safe for most women, although each individual woman has to have a discussion with her own doctor about oral contraceptives and different formulations, but I think this study reinforces that low-dose monophasic pills did not increase risk and was consistent with the CARE study," Pederson said. "And, in the small numbers of women who took those three types of pills that are rarely used, I don't think that generalizations can be made."
The new findings were published today in the journal Cancer Research.