Women with a history of endometriosis are at a significantly increased risk of developing several types of ovarian cancers, according to a new study published in the Lancet Oncology.
Endometriosis occurs when the cells from the lining of the uterus grow in other areas of the body, according to the National Institutes of Health. About 10 percent of women in their childbearing years experience it. It can cause pain, irregular bleeding and make it difficult to conceive.
The new research found that women with endometriosis have a three times higher risk of developing clear-cell ovarian cancer (which accounts for less than 5 percent of all ovarian cancer cases) and twice the risk of developing endometrioid tumors.
"Our data, taken with the other published data on the link between ovarian cancer and endometriosis strongly suggests a causal relationship, with endometriosis being a precursor lesion for these three types of ovarian cancer," Dr. Celeste Leigh Pearce, lead author of the study and a preventive medicine researcher at University of Southern California, told ABCNews.com.
Researchers analyzed the link between endometriosis and ovarian cancer rates from data compiled by the Ovarian Cancer Association Consortium, a forum of investigators of case-control studies on the cancer. Tuesday's published study included data from more than 23,000 women with ovarian cancer.
"This excellent study brings home the point to all primary care physicians that women with endometriosis, surgically proven or self-reported by symptoms, deserve to have available all options to limit this ectopic endometrial growth," said Dr. Diane Harper, director of the Gynecologic Cancer Prevention Research Group at the University of Missouri-Kansas City.
A woman with a mother or sister with endometriosis is significantly more likely to contract endometriosis than other women, according to the NIH. Other risks of developing the condition include beginning menstruating at an early age, never having children, and frequent and long-lasting periods. The most telling sign of endometriosis is pain-during and before menstruation, sexual intercourse, and found in the abdomen, lower back and pelvic area.
While this is not the first time that a link between endometriosis and ovarian cancer has been studied, Dr. Mark Einstein, director of gynecologic oncology at Montefiore Medical Center, said the combining of studies offers a better understanding of the strength of the association between endometriosis and ovarian cancers.
"This association is higher than I had previously known, so this is new information for those of us who take care of women that suffer from this aggressive subtype of cancer," said Einstein.
Authors warned that most women who suffer from endometriosis never develop ovarian cancers, but the findings should alert patients and physicians of the high risks.
"Women should keep in mind that endometriosis is far more common than ovarian cancer," said Pearce. "Most women with endometriosis do not go on to develop ovarian cancer. Women with endometriosis should discuss these findings with their physician."
Dr. Diane Yamada of the Society for Gynecologic Oncology Communications Committee said that, while the study should not be a cause of alarm for women with endometriosis, the research "may allow for an opportunity to identify symptoms associated with another disease process, which may help identify these patients."
"The difficult question is how should patients with endometriosis be screened?" said Yamada. "It is difficult to make the jump to formulating a blanket statement for screening for women with endometriosis."
Recent studies have even found that ultrasounds and blood tests intended to screen for ovarian cancer actually did more harm than good by undergoing unnecessary follow-up treatments and surgeries. At this point, Yamda said it would be a "leap of faith" to recommend that women should undergo rigorous screening, but the information offers new clues on how and who to screen to prevent the cancer, which causes about 15,000 American deaths each year, according to the American Cancer Society.
"Screening programs for ovarian cancer are not currently effective, but that may change in the future and women with endometriosis," said Pearce. "[It] may represent a population for whom screening may be appropriate."
ABC News' Dr. Richa Shukla contributed to this report.