Abstract B8: Molecular subtyping of epithelial ovarian cancer reveals connections to intrinsic breast cancer subtypes

Abstract Aim: Epithelial ovarian cancer is one of the most lethal female cancers. It is a heterogeneous group of neoplasms and the different histologic subtypes are thought to constitute separate disease entities. Efforts have been made to characterize ovarian cancers further and molecular subgroups that correlate to clinical features have been reported, but are still not in clinical use (Tothill et al., Clin Cancer Res, 2008). The subgroups, called C1-C6, represent serous and endometrioid ovarian tumors with the C1-C2 and C4-C5 subgroups characterizing high-grade serous tumors and correlated to a worse prognosis. The C3 and C6 subtypes represent borderline and low-grade tumors and show a favorable prognosis. We aimed to further outline and refine the genetic differences between malignant, benign and borderline ovarian tumors and to investigate similarities between ovarian cancer and the well described intrinsic subtypes of breast cancer (Perou et al., Nature, 2000). Materials and methods: Global gene expression profiling (Illumina HT-12 bead arrays) was applied to 72 fresh-frozen serous ovarian tumors (37 adenocarcinomas, 17 adenomas, 5 borderline tumors,13 biological replicates) collected in the ovarian tumor tissue biobank at Skane University Hospital, Sweden (2004-2011). We performed nearest centroid classification of our tumors for the molecular subtypes of ovarian cancer (“C-signatures”) as well as for the intrinsic subgroups of breast cancer (luminal A, luminal B, basal-like, normal-like, and HER2) using the genes from Hu et al. (BMC Genomics, 2006). The results were validated by performing nearest centroid classification of the intrinsic breast cancer subtypes and the C-signatures on the ovarian tumors in the Tothill cohort as well. Results: Our malignant tumors correlated significantly to the basal-like breast cancer subtype (p<0.001) and to the ovarian C1, C2 and C4 signatures (p=0.020). The basal-like tumors, in turn, correlated significantly to the C2 and C4 signatures (p=0.019 and p=0.001, respectively), thus supporting a link between molecular subtypes of ovarian and breast cancers. The borderline and benign tumors showed a significant correlation to the normal-like breast cancer subtype and the ovarian C3 signature, and these signatures also correlated significantly with each other (p<0.001). These findings were supported when the breast cancer subtypes were applied to the Tothill cohort; the basal-like subtype correlated significantly to the C2 signature and the normal-like subtype to the C3 signature (p<0.001). Of interest, there was a tendency towards worse prognosis among malignant tumors that correlated to the basal-like breast cancer subtype compared to the other malignant tumors, which is in line with similar findings in breast cancer. All reported p-values are calculated using Fischer's Exact Test. Conclusion: Both epithelial ovarian cancers and breast cancers are heterogeneous diseases, nevertheless they share many similarities such as hormonal influence and varying long-term prognosis. Our novel findings support a link between previously reported molecular subtypes in ovarian cancer and the well-established intrinsic subtypes of breast cancer, which could potentially be of use for further investigations of biomarkers in ovarian cancer and new thinking regarding the use of chemotherapeutic agents as well as targeted treatments. Citation Format: Jenny-Maria Jönsson, Mev Dominguez-Valentin, Ida Johansson, Siker Kimbung, Mats Jönsson, Anna Måsbäck, Susanne Malander, Mef Nilbert. Molecular subtyping of epithelial ovarian cancer reveals connections to intrinsic breast cancer subtypes. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr B8.