Adenomatoid tumor of the genital tract: Evidence of mesenchymal cell origin

The objective of this study was to re-examine the histogenesis of adenomato id tumors. This benign neoplasm is characterized by gland-like structures w ith a pseudodinfiltrative pattern, usually involving fibromuscular tissue a t a certain distance from an overlying surface mesothelium. Twenty cases of adenomatoid tumors and four cases of reactive submesothelia l lesions, characterized by marked proliferation of subserosal mesenchymal cells, were reviewed. Nineteen of twenty adenomatoid tumors, including lesi ons with ill-defined borders, showed no connection with surface mesothelium . At the periphery of small tumors, isolated glands, clusters of epithelioi d cells and single epithelioid, and spindled cells showing no connection to adjacent glands or cell clusters were identified. The tumor cells shared f eatures with reactive subserosal stromal cells including an infiltrative pa ttern and histochemical and immunohistochemical properties. The differences between adenomatoid tumors and reactive submesothelial tiss ue are quantitative in nature: predominant amount of spindled cells in reac tive submesothelial lesions, and predominant amount of glandlike structures in adenomatoid tumors. It is proposed that adenomatoid tumors arise from p luripotent mesenchymal cells that differentiate toward submesothelial cells and eventually mesothelial cells. This differentiation is probably induced by the adjacent submesothelial cells.