Abstract
Among epithelial ovarian cancer, clear cell carcinoma is common for chemo-resistance and high mortality. This cancer arises from benign ovarian endometrioma (OE), which is a high oxidative stress environment due to the cystic retention of menstrual blood produced during menstruation and the "iron" liberated from the cyst. There has been strong evidence that the iron concentration in OE decreases when they become cancerous. A decrease in iron concentration is a necessary condition for the formation of cancer. However, the mechanism of carcinogenesis is not yet clear. In the current study, the bacterial flora in endometriosis-associated ovarian cancer (EAOC), including clear cell carcinoma, and their origin, OE, were investigated using next-generation sequencing. The Shannon index in the genus level was significantly higher in EAOC than in OE fluids. Among several bacterial flora that were more abundant than benign chocolate cysts, a number of bacterial species that correlate very well with iron concentrations in the cysts were identified. These bacterial species are likely to be associated with decreased iron concentrations and cancer development.