S100-positive stroma in salivary gland basal cell adenoma: recent progress and future perspectives.

Basal cell adenoma (BCA) with S100-positive stroma exhibits tricellular differentiation, consisting of bilayered epithelial cells and S100-positive spindle-shaped stromal cells. While the neoplastic nature of the stromal component has been supported by multiple lines of evidence, its myoepithelial origin, suggested by ultrastructural analysis, has not yet been confirmed by other methodological approaches. This mini-review summarizes the key findings of ultrastructural, immunohistochemical and molecular studies with a particular emphasis on the biological nature of the stromal component. Elucidating the lineage and molecular profile of this unique stroma may contribute to a more refined classification and enhance our understanding of salivary gland tumors.