Unique miRNA profiling of squamous cell carcinoma arising from ovarian mature teratoma: comprehensive miRNA sequence analysis of its molecular background

Owing to its rarity, the carcinogenesis and molecular biological characteristics of squamous cell carcinoma arising from mature teratoma remain unclear. This study aims to elucidate the molecular background of malignant transformation from the aspects of microRNA (miRNA) profiling. We examined 7 patients with squamous cell carcinoma and 20 patients with mature teratoma and extracted their total RNA from formalin-fixed paraffin-embedded tissues. Then we prepared small RNA libraries and performed comprehensive miRNA sequencing. Heatmap and principal component analysis revealed markedly different miRNA profiling in cancer, normal ovarian and mature teratoma tissues. Then we narrowed down cancer-related miRNAs, comparing paired-cancer and normal ovaries. Comparisons of cancer and mature teratoma identified two markedly upregulated miRNAs (miR-151a-3p and miR-378a-3p) and two markedly downregulated miRNAs (miR-26a-5p and miR-99a-5p). In addition, these findings were validated in fresh cancer tissues of patient-derived xenograft (PDX) models. Moreover, several miRNAs, including miR-151a-3p and miR-378a-3p, were elevated in the murine plasma when tumor tissues were enlarged although miR-26a-5p and miR-99a-5p were not elucidated in the murine plasma. Finally, we performed target prediction and functional annotation analysis in silico and indicated that targets genes of these miRNAs markedly correlated with cancer-related pathways, including 'pathway in cancer' and 'cell cycle'. In conclusion, this is the first study on miRNA sequencing for squamous cell carcinoma arising from mature teratoma. The study identified four cancer-related miRNAs that were considered to be related to the feature of malignant transformation. Moreover, miRNAs circulating in the murine plasma of the PDX model could be novel diagnostic biomarkers.