The most common sexually transmitted disease can double a woman’s risk of ovarian cancer, according to new research released Thursday.

Women who had chronic chlamydia infections had twice the risk of ovarian cancer compared to women with no evidence of ever having been infected, researchers are expected to report at a meeting of the American Association for Cancer Research in April.

“Our data is lending support for there being a role of pelvic inflammatory disease in ovarian cancer and the prime cause of pelvic inflammatory disease, particularly in the U.S., is chlamydia infection,” the National Cancer Institute’s Britton Trabert told a briefing ahead of the meeting.

“We are seeing a doubling in ovarian cancer risk with a prior history of pelvic inflammatory disease.”

Ovarian cancer is not common, but it will be diagnosed in more than 21,000 American women this year and it will kill more than 14,000. It is the fifth leading cause of cancer deaths among women, killing 55 percent of patients within five years.

Chlamydia is very common. More than 1.5 million Americans have chlamydia, the Centers for Disease Control and Prevention reports. Chlamydia is easily treated with antibiotics, but it often causes no symptoms, so people can be infected for months or even years and not know it.