Trabert B, et al. - Given the association between pelvic inflammatory disease (PID) and ovarian cancer risk, researchers investigated how Chlamydia trachomatis and other infectious agents influence the development of ovarian cancer via evaluating the association of serologic markers with incident ovarian cancer using a staged approach in two independent populations. They performed a case–control study in Poland (244 ovarian cancers/556 control subjects) and a prospective nested case–control study in the PLCO Cancer Screening Trial (160 ovarian cancers/159 control subjects). The two independent populations displayed an association of antibodies against prior/current C. trachomatis (Pgp3) with a doubling in ovarian cancer risk. However, no correlation of markers of other infectious agents was observed. This study thereby establishes that PID is associated with ovarian cancer.