A small study has found that women who took a well-known drug treatment for endometriosis were nearly three times more likely to develop ovarian cancer than patients who didn't take the medication.
The findings are provocative, but much more research needs to be done before they can be considered definitive, experts said.
Dr. Roberta Ness of the University of Pittsburgh Graduate School of Public Health presented the preliminary findings yesterday in Miami at the annual meeting of the Society of Gynecologic Oncologists.
The research team pooled data from two studies conducted around Philadelphia, and Hawaii and Los Angeles. Although several thousand women participated in the trials, only about 400 had endometriosis. Fewer than a tenth of them were treated with the drugs danazol or leuprolide.
The patients who took danazol, a drug developed many years ago specifically to treat endometriosis, were 2.7 times more likely to develop ovarian cancer than those who didn't take the medication. Leurpolide did not elevate the risk.
"When we first found this, I urged the National Cancer Institute to try to follow up on these findings," Ness said. "They have some ongoing studies in large populations that I think can help to address the same question. It's terribly important to know whether this is real or not."
But, Ness added, "I would urge clinicians to consider this information and the limitations of this preliminary study" when prescribing drugs for endometriosis patients.
Dr. Holly Gallion, an expert in gynecologic oncology at Magee-Womens Hospital, said that the data should be interpreted very cautiously.
"The numbers are exceptionally small," she said. "Even if this is real and confirmed in larger studies ... then the increased risk is small."
The drug is no longer a first-line treatment for endometriosis, she noted. Oral contraceptives are more commonly prescribed.
The overall lifetime risk of ovarian cancer ranges from one out of 70 to one out of 100, Gallion said. Women who have a family history of the disease have a much higher risk, ranging from 16 to 45 percent.
Endometriosis is a condition in which uterine lining-like tissue implants elsewhere in the body, such as on the ovaries. Because it is endometrial tissue, the lesions respond to the hormonal cues of the menstrual cycle.
"That cycling and bleeding is what causes the pain, inflammation and infertility associated with endometriosis," Ness said.
Danazol also is used to treat conditions including fibrocystic breast disease or abnormal menstrual bleeding due to uterine fibroids. It is not known whether women who took danazol in those circumstances are at greater risk.
