A Case Study of a Small Ovarian Teratoma: Histological and Molecular Characteristics

Background: Ovarian teratomas are ovarian tumors composed of three germ layers. They are rarely detected early, and the early stages have neither been reported often nor well characterized. Case presentation: We describe a teratoma measuring 2 × 0.8 mm, one of 1254 consecutive ovarian teratomas diagnosed at three institutions. This is the smallest ovarian teratoma reported in the available literature in English. The teratoma bud contained primitive glandular structures, mesoderm-like cells, cord- and sinus-like structures, and surface cells that were flat-to-cuboidal. To characterize this small teratoma, RNA sequencing was performed; 60 RNAs involved in embryonic morphogenesis were detected. The genes SHH , SOX2 , and SOX9 , which are involved in maturation and differentiation of the early embryo, were expressed in the tumor and evaluated with RNA in situ hybridization. We found distinct expression patterns corresponding to the histological components of the teratoma bud that were identified in formalin-fixed paraffin-embedded sections. Conclusions: : The results of the histological and molecular analyses indicated that ovarian teratomas contain rudimentary organ-like features in the early stage of development, and as the tumor grows, these components differentiate into well-developed somatic tissues through the co-expression of RNAs involved in embryonic morphogenesis.