IMP3 expression in human ovarian cancer is associated with improved survival

The insulin-like growth factor-II mRNA-binding protein IMP3 plays an important role in embryogenesis and recent reports suggest an involvement in tumorigenesis. Although IMP3 expression has been well studied in mouse and human fetal and adult gonads, its role in ovarian cancer is unknown. We investigated the expression of IMP3 at protein and mRNA levels in a cohort of primary ovarian carcinomas and in 11 ovarian cancer cell lines. Western blot analysis revealed an expression of IMP3 in all ovarian cancer cell lines and immunohistochemistry demonstrated a positive cytoplasmic staining in 32 of 68 carcinomas (47%). In contrast, epithelium of borderline tumors, as well as, benign ovarian lesions and normal ovaries exhibited only weak or no IMP3 expression. In univariate Kaplan-Meier analysis, IMP3 protein expression was significantly associated with better overall survival (P = 0.048). To confirm these findings, we further determined IMP3 mRNA expression in 43 ovarian cancer specimens by real time quantitative reverse transcription-polymerase chain reaction. A significant correlation between protein and mRNA levels (r = 0.414, P = 0.006), as well as a correlation of IMP3 mRNA expression with patient overall survival (P = 0.044), was observed. Our results demonstrate that IMP3 is expressed in a subpopulation of ovarian cancer and a marker of good prognosis.