Adenomyosis and peritoneal endometriosis are common gynecologic lesions; they are characterized by aberrant locations of normal-appearing endometrium in myometrium and peritoneal surface, respectively. Both ectopic lesions are speculated to originate from uterine eutopic endometrium, which is composed of epithelium and stroma, but how these two different tissue types co-evolve in ectopic locations remain unclear. Here, we analyzed exome-wide mutations and global methylation in microdissected epithelium and stroma separately in paired adenomyosis, peritoneal endometriosis, and endometrium to investigate their relationship. Analyses of somatic mutations and their allele frequencies indicate mono-clonal development not only in epithelium but also in the stroma of adenomyosis and peritoneal endometriosis. Our preliminary phylogenetic study suggests a plausible clonal derivation in epithelium and stroma of both ectopic and eutopic endometrium from the same founder epithelium-stroma progenitor cells. While a patient-specific methylation landscape is evident, adenomyosis epithelium and stroma can be distinguished from normal-appearing eutopic endometrium and epigenetically less homogenous. In summary, endometrial stroma, like its epithelial counterpart, could be clonal and both ectopic and eutopic endometrium following divergent evolutionary trajectories. Our data also warrant future investigations into the role of endometrial stroma in the pathobiology of endometrium-related disorders.

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