Endometriosis and pelvic inflammatory disease are considered to be risk factors for ovarian cancer, as dysbiosis likely contributes to ovarian cancer development via chronic inflammation and immune response alteration. Therefore, we hypothesized that pelvic inflammatory disease predisposes to ovarian cancer development in women with endometriosis.
We selected patients who were diagnosed with endometriosis or pelvic inflammatory disease between January 1, 2000, and December 31, 2015 in a 2-million longitudinal health and welfare database in Taiwan, with cancer and death registries. Patients were divided into five groups: those with (1) endometriosis, (2) pelvic inflammatory disease, (3) endometriosis diagnosed before pelvic inflammatory disease, and (4) pelvic inflammatory disease diagnosed before endometriosis, as well as (5) healthy women. Propensity score matching with inverse probability of treatment weighting was used to adjust for covariates across the study groups.
The risk of ovarian cancer was significantly higher in women with endometriosis and subsequent pelvic inflammatory disease than in those with endometriosis alone (hazard ratio 8.07; 95% confidence interval, 4.53-14.37; P<0.001). The same result was found for ovarian cancer incidence per 1,000 person-years.
Our data show that pelvic inflammatory disease is associated with cancer development in women with preexisting endometriosis.

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