A study published by an international consortium of researchers in The Lancet links endometriosis, a fairly common gynecological condition for women, with ovarian cancer.

Patsy McConnell, 77, was diagnosed with the condition 20 years ago, when she saw her doctor to report some problems with her menstrual cycle. 

"I had extra bleeding, and I had a few clots, that sort of thing," she said.

Endometriosis is characterized by the accumulation of cells which should be shed during menstruation. "Instead of the tissue from the uterine lining coming out to the outside, some of this can reflux back through the tubes," described Dr. Andrew Berchuck, an obstetrician/gynecologist at Duke University. 

Those extra cells can start growing on the ovaries, in the pelvic area and on other organs. There's no cure, but endometriosis can be medically managed.

Berchuck and an international consortium analyzed 45 studies to see if endometriosis is a risk factor for ovarian cancer. "We found very clear, definitive proof that endometriosis increases the risk of certain types of ovarian cancer," he said.

He says most women with endometriosis won't develop ovarian cancer, though McConnell was diagnosed and underwent chemotherapy for it two years ago.

"I had to have a complete hysterectomy, 24 lymph nodes removed," she said.

The findings may hasten the search for ways to screen women for endometriosis and identify those at greatest risk of ovarian cancer.

"Then we can start to talk about interventions that might decrease the risk of progression of endometriosis to cancer in these women," Berchuck said.

Berchuck expects that future screening for endometriosis may come from improved imaging technology or by detecting blood markers for the disease.