Purpose: High-grade serous ovarian cancers are heterogeneous not only in terms of clinical outcome but also at the molecular level. Our aim was to establish a novel risk classification system based on a gene expression signature for predicting overall survival, leading to suggesting novel therapeutic strategies for high-risk patients.Experimental Design: In this large-scale cross-platform study of six microarray data sets consisting of 1,054 ovarian cancer patients, we developed a gene expression signature for predicting overall survival by applying elastic net and 10-fold cross-validation to a Japanese data set A (n ¼ 260) and evaluated the signature in five other data sets. Subsequently, we investigated differences in the biological characteristics between high-and low-risk ovarian cancer groups.Results: An elastic net analysis identified a 126-gene expression signature for predicting overall survival in patients with ovarian cancer using the Japanese data set A (multivariate analysis, P ¼ 4 Â 10 À20 ). We validated its predictive ability with five other data sets using multivariate analysis (Tothill's data set, P ¼ 1 Â 10 À5 ; Bonome's data set, P ¼ 0.0033; Dressman's data set, P ¼ 0.0016; TCGA data set, P ¼ 0.0027; Japanese data set B, P ¼ 0.021). Through gene ontology and pathway analyses, we identified a significant reduction in expression of immune-response-related genes, especially on the antigen presentation pathway, in high-risk ovarian cancer patients.Conclusions: This risk classification based on the 126-gene expression signature is an accurate predictor of clinical outcome in patients with advanced stage high-grade serous ovarian cancer and has the potential to develop new therapeutic strategies for high-grade serous ovarian cancer patients.

Maximum SUV on preoperative FDG-PET/CT in ovarian epithelial cancer differs according to histologic type. In clear cell AC, SUVmax may represent a prognostic factor.