The Origin of Epithelial Neoplasms of the Ovary: An Alternative View

Preclinical Models of Ovarian Cancer: Pathogenesis, Problems, and Implications for Prevention

Preclinical models are relatively underutilized and underfunded resources for modeling the pathogenesis and prevention of ovarian cancers. Several reviews have detailed the numerous published models of ovarian cancer. In this review, we will provide an overview of experimental model systems, their strengths and limitations, and use selected models to illustrate how they can be used to address specific issues about ovarian cancer pathogenesis. We will then highlight some of the preclinical prevention studies performed to date and discuss experiments needed to address important unanswered questions about ovarian cancer prevention strategies.

DNA Methylome Analyses Implicate Fallopian Tube Epithelia as the Origin for High-Grade Serous Ovarian Cancer

High-grade serous ovarian cancer (HGSC) is the most common and lethal form of epithelial ovarian cancer (EOC). Two distinct tissues have been suggested as the tissue of origin: ovarian surface epithelia (OSE) and fallopian tube epithelia (FTE). We hypothesized that the DNA methylome of HGSC should more closely resemble the methylome of its tissue of origin. To this end, we profiled HGSC (n = 10), and patient-matched OSE and FTE (n = 5) primary fresh-frozen tissues, and analyzed the DNA methylome using Illumina 450K arrays (n = 20) and Agilent Sure Select methyl-seq (n = 7). Methylomes were compared using statistical analyses of differentially methylated CpG sites (DMC) and differentially methylated regions (DMR). In addition, methylation was evaluated within a variety of different genomic contexts, including CpG island shores and Homeobox (HOX) genes, due to their roles in tissue specification. Publicly available HGSC methylome data (n = 628) were interrogated to provide additional comparisons with FTE and OSE for validation. These analyses revealed that HGSC and FTE methylomes are significantly and consistently more highly conserved than are HGSC and OSE. Pearson correlations and hierarchal clustering of genes, promoters, CpG islands, CpG island shores, and HOX genes all revealed increased relatedness of HGSC and FTE methylomes. Thus, these findings reveal that the landscape of FTE more closely resembles HGSC, the most common and deadly EOC subtype.

IMPLICATIONS

DNA methylome analyses support the hypothesis that HGSC arise from the fallopian tube and that due to its tissue-specificity and biochemical stability, interrogation of the methylome may be a valuable approach to examine cell/tissue lineage in cancer. Mol Cancer Res; 14(9); 787-94. ©2016 AACR.