Chlamydia is the most commonly reported sexually transmitted infection in the United States, and women who contract it may be at an increased risk for developing ovarian cancer, according to research to be presented at the American Association for Cancer Research (AACR) Annual Meeting.

Researchers in the Division of Cancer Epidemiology and Genetics at the National Cancer Institute (NCI) gathered data from two different studies. The first was a Polish study of 834 women, of which, 278 were diagnosed with ovarian cancer, and the rest were matched controls. The other study was the NCI-sponsored Prostate, Lung, Colorectal, and Ovarian Cancer (PLCO) Screening Trial, which was a nested case-control study with pre-diagnosis blood draws. This study had 160 women who ended up with an ovarian cancer diagnosis, and 159 controls.

Both studies found that women with higher levels of Pgp3 antibodies — which are a typical indication for chlamydia infection – were more likely to receive an ovarian cancer diagnosis.

When researchers then created an even more stringent cut point for Pgp3 antibody expression, indicating chronic and/or persistent chlamydia, the likelihood for ovarian cancer doubled.

Interestingly, when the studies examined antibodies associated with other diseases, such as HIV, herpes simplex virus, and hepatitis B and C, the researchers found no increase in ovarian cancer risk.

But one aspect of chlamydia that might set it apart from other infections is that it could cause pelvic inflammation, which has been linked to ovarian cancer in previous studies.

"Pelvic inflammatory disease is caused when bacteria infects the upper-genital tract,” lead study author Britton Trabert, Ph.D., M.S., Earl Stadtman Investigator at the NCI, said during the AACR Annual Meeting media preview webinar. “Pelvic inflammatory disease has been associated with ovarian cancer, and chlamydia infection is the leading cause of pelvic inflammatory disease in the developed world.”

Trabert said that she’d like to delve into this theory a bit further, studying larger populations to confirm these findings and see if there is a correlation between chlamydia and specific types of ovarian cancer.

Down the line, these findings might lead to ovarian cancer risk reduction by treating chlamydia and pelvic inflammatory disease, said Trabert

This is particularly important because most ovarian cancers are diagnosed in later stages since they are not easy to find and diagnose. Knowing risk factors to prevent the disease or diagnose it at an earlier stage can drastically improve outcomes in this patient population.

"Replication of these results is necessary,” Trabert said. “This corroborated support for future studies to evaluate the possibility of ovarian cancer risk reduction through treatment of chlamydia and pelvic inflammatory disease."