In order to investigate a possible role of this pathway in EOC, we performed semi-quantitative RT-PCR to investigate the expression of PIWIL1, PIWIL2, PIWIL3, PIWIL4 and MAEL in advanced stage serous EOC (n = 25), benign ovarian tumors (n = 19) and normal ovarian tissue (n = 8) (Table 1, Table S3 and Fig. 1A, B). Here, PIWIL2 is linked to ovarian benign neoplasm.