Adenomatoid tumor of the genital tract: evidence of mesenchymal cell origin.

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