Adenomyoma of the uterus is a biphasic nodular lesion composed of a mesenchymal component with smooth muscle differentiation and a glandular epithelium. The neoplastic nature of uterine
adenomyomas has been controversial because some are considered to be nodular
adenomyosis. MED12 mutations are involved in the pathogenesis of uterine
smooth muscle tumors (
leiomyomas and
leiomyosarcomas) and biphasic
tumors of the breast (
fibroadenomas and
phyllodes tumor). To investigate the histogenesis of uterine
adenomyomas, we performed pathological and genetic analyses, including Sanger sequencing of MED12. In total, 15 cases of uterine
adenomyomas were retrieved and assessed for clinicopathological factors. Immunohistochemistry for smooth muscle actin,
desmin, and CD10 was performed. Exon 2 of MED12 was Sanger sequenced using
DNA obtained by macrodissection of the
adenomyomas. For cases that were positive for somatic MED12 mutations, we next performed microdissection of the mesenchymal and epithelial components. The
DNA extracted from each component was further analyzed for MED12 mutations. MED12 mutations were detected in two
adenomyomas (2/15, 13%), all in a known hot spot (
codon 44). In both lesions, MED12 mutations were detected in multiple spots of the mesenchymal component. The epithelial component did not harbor MED12 mutations. The relatively low frequency of MED12 mutations suggests that not all
adenomyomas are
leiomyomas with entrapped glands. However, the results of our study suggest that a subset of uterine
adenomyomas are true mesenchymal
neoplasms.