Oral contraceptives offer long-term ovarian cancer protection

Reduction in risk can continue for more than 30 years after termination of use.

During the last 50 years, oral contraceptives have prevented 200,000 incident cases and 100,000 deaths from ovarian cancer, according to researchers from the Collaborative Group on Epidemiological Studies of Ovarian Cancer.

“In the long term, the pill is protective against cancer,” Valerie Beral, MD, director of the Cancer Research Epidemiology Unit at Oxford University, England, told HemOnc Today.

To determine the duration of disease protection provided by oral contraceptives, the group analyzed data from 45 epidemiological studies of ovarian cancer conducted in 21 countries. Women with malignant epithelial or nonepithelial ovarian cancer (n=23,257) were compared with controls (n=87,303).

Affirming facts

Oral contraceptive users included 7,308 (31%) cases and 32,717 (37%) controls, whose average lengths of use were 4.4 and five years. The researchers found that relative risk for ovarian cancer was greatly reduced in oral contraceptive users, and a longer duration of use produced a lower risk. Each five years of use resulted in a 20% relative risk reduction; the relative risk was halved among women taking oral contraceptives for about 15 years.

On average, ovarian cancer diagnoses came about 20 years after women had first used oral contraceptives. The mean age at diagnosis was 56 years.

“Though there is a short-term increase in [the risk for] breast cancer and cancer of the cervix—which has been recorded before—this protection against cancer of the ovary is more long lasting and more profound than any increase. So, on balance, there is no increase in cancer among women who take the pill,” Beral said.

Though relative risks were lower in women who had recently used oral contraceptives, risk reduction continued for 30 or more years after use.

Times change

A correlation had previously been found between calendar year of use and the dosage of estrogen in oral contraceptives. In the 1960s, oral contraceptives contained a high dosage of estrogen, about 100 mcg or more, but by the 1980s the dosage of estrogen was cut significantly to about 30 mcg or less.

Due to the change in estrogen levels of oral contraceptives throughout the years, researchers grouped women according to mid-year of use: before 1970, 1970 to 1979, and 1980 or after. Women were also classified by the calendar year of first and last use, according to the researchers.

Among women with ovarian cancer, almost 40% had a mid-year oral contraceptive use in the 1960s, whereas 13% had a mid-year use in the 1980s or later, the researchers wrote. Time since oral contraceptive cessation differed between the two groups (25 years vs. five years), but calendar year of first and last use had no obvious effect on ovarian cancer risk.

“The dose of estrogen appeared not to have any effect on ovarian cancer risk. It appeared that the protection was similar for all types of estrogen dose, as far as we can tell,” Beral said. – by Stacey L. Adams

For more information:

• Collaborative Group on Epidemiological Studies of Ovarian Cancer. Ovarian cancer and oral contraceptives: collaborative reanalysis of data from 45 epidemiological studies including 23,257 women with ovarian cancer and 87,303 controls. Lancet. 2008;371:303-314.

This a meta-analysis of many prior studies, and is not, as we say, “new news.” This has been known for a long time. When I saw the crawl on CNN, I remember thinking that they were presenting it like it was some big discovery. But in actuality, this is a reaffirmation of many past case control studies that have repeatedly demonstrated that the risk for developing epithelial ovarian cancer in women who take the birth control pill is appreciably lowered, and it is the only means of chemo-protection that we have for the disease. So, it is an important observation; that is, women who take the pill, even discontinuously, for up to five years or longer have about a 50% lower risk for getting ovarian cancer than women who do not. Now, if you add on top of that women who have had a couple of babies and have also taken the pill for five years or longer, again, not necessarily for five years at the same time but spread out during their reproductive years, their risk for ovarian cancer may be reduced by up to 70%. So, essentially, the researchers of this study went back and compiled all the other data that had repeatedly shown that this was the case, and it reaffirmed that fact in a clear way.

I am pleased to see that at least this information is becoming better promulgated because it is an important public health observation; that, short of removing ovaries and fallopian tubes in women who may be at risk for the disease, this is the only way we know, at this point, to reduce the risk for these types of cancer.

The general public needs to be aware of this information; it is an important finding because we have no means of early detection in ovarian cancer. When a patient has a choice of contraceptives, if one of their concerns is ovarian cancer, they should strongly consider the use of the birth control pill as they are doing their family planning. And given the option between different types of pills, this should be high on their list.

It is also important for practitioners who prescribe birth control and participate in the process of family planning on a general level. Those physicians should use this information as a means by which they counsel patients as to the advantages of the birth control pill by informing patients that it lowers the risk for ovarian and endometrial cancers and, based on now considerable data, there is no increased risk for breast cancer.

– Jonathan S. Berek, MD, MMS

Professor and Chair, Department of Obstetrics and Gynecology at Stanford University School of Medicine