Identification of differentially expressed proteins associated with recurrence in ovarian endometriotic cysts. 
The objective of this study was to identify proteins that are differentially expressed in the cystic wall tissues of ovarian endometriotic cysts, simple ovarian cysts, and in normal ovarian tissues.  Specimens of ovarian endometriotic cyst wall tissue, simple ovarian cyst wall tissue, and normal ovarian tissue (six specimens per group) were collected from patients who received gynecologic surgery, respectively.  Differentially expressed proteins related to the ovarian endometriotic cysts were screened by use of isobaric tags for relative and absolute quantitation (iTRAQ) combined with functional annotation and bioinformatics analyses.  All differentially expressed proteins related to cysts were validated using immunohistochemistry methods in recurrent and non-recurrent ovarian endometriotic cyst.  A total of 359 proteins were identified as up-regulated in ovarian endometriotic cyst groups when compared with both the normal ovary and simple ovarian cyst groups.  The levels of 27 proteins were >two-fold higher in the ovarian endometriotic cyst group than that in the other two groups.  Of note, the five most significantly upregulated proteins were Charcot-Leyden Crystal Galectin (CLC), Defensin, alpha 1 (DEFA1), S100 calcium-binding protein A9 (S100A9), S100 calcium-binding protein A8 (S100A8), and Ferritin Light Chain (FTL).  Immunohistochemistry results showed that the changes of S100A9 and S100A8 were consistent with the results shown by iTRAQ.  However, no similarity of CLC, DEFA1, and FTL proteins was found between iTRAQ and immunohistochemistry.  The ratio of patients with abnormally high S100A9 and S100A8 expression in the recurrent ovarian endometriotic cyst group was significantly higher than that in the non-recurrent group (P < 0.05).  Our data identify differentially expressed proteins S100A9 and S100A8, and suggest they may serve as novel molecular markers to predict postoperative recurrence of an ovarian endometriotic cysts. Abbreviations: iTRAQ: isobaric tags for relative and absolute quantitation; HPRD: Human Protein Reference Database; GO: Gene Ontology; KEGG: Kyoto Encyclopedia of Genes and Genomes; EM: Endometriosis; COX-2: cyclooxyenase-2; NF-kB: nuclear factor kappa-B; PR-B: progesterone receptor type B.