Use of fertility drugs does not increase a woman's risk of getting ovarian cancer said researchers in the American Journal of Epidemiology (Vol. 155, No. 3: 217-224).

On the other hand, the scientists did find an association between ovarian cancer and certain causes of infertility itself, such as endometriosis.

"Some women who receive fertility treatments develop ovarian cancer because of underlying conditions that cause infertility, not because of the treatments themselves," said Roberta Ness, MD, MPH, of the University of Pittsburgh's School of Public Health.

"Overall, the study offers very good news in that it will help make many women feel more comfortable about their choice to take fertility drugs," Ness said. She added that several other large studies will soon be completed that may put the issue to rest.

Ever since two American studies a decade ago found a strong link between use of fertility drugs and ovarian cancer, there has been "tremendous concern and anxiety among women who use fertility drugs," said Ness. "They feel they have to make a terrible trade-off between wanting to have a baby and putting themselves at risk for an awful disease."

It made biological sense that fertility drugs might promote cancer because they increase the number of ovulations a woman has, and so the studies received wide public attention, said Ness. But they were flawed "in that they were not designed to answer the specific question of whether fertility drugs cause ovarian cancer," she said.

So Ness and US, European, and Australian researchers combined data on infertility and fertility drug use from eight studies conducted between 1989 and 1999. Seven of the studies had not yet been published. The data included 5,207 women with ovarian cancer and 7,705 women without cancer.

Results showed that infertile women who had used fertility drugs were no more likely to develop ovarian cancer than those who had never used these drugs. But researchers also found that women who spent more than five years trying to conceive were at a 2.7-fold higher risk for ovarian cancer than normally fertile women.

Women who were infertile because they had a condition called endometriosis were most likely to develop ovarian cancer. In endometriosis, tissue from the lining of the uterus (or womb) grows outside of the womb. It is common for it to adhere to the ovaries. When this happens, it can interfere with their function.

Ness theorizes that the local inflammation with endometriosis may play a role in ovarian cancer. Some women may have been infertile because of other unknown causes which may also play a role in ovarian cancer.

It's important to put the study's negative findings into perspective, said Carmen Rodriguez, MD, MPH, a senior epidemiologist at the American Cancer Society and director of the LifeLink Blood Collection Study.

Rodriguez said that while infertility itself may elevate the risk of ovarian cancer — a finding she has made in her own research — women should understand that both primary infertility, which is the inability to conceive, as well as ovarian cancer itself, are both uncommon conditions.

It has long been known that pregnancy protects against ovarian cancer, she said. In this study, women who were able to become pregnant, even if they did not give birth, were not at a higher risk for cancer.

The results of this study should be reassuring, but also carry a warning to women unable to conceive. They do have an increased risk of ovarian cancer, but are not increasing that risk by using fertility drugs. Indeed, if they are successful in becoming pregnant, they may be lowering their risk.