The altered expression of alpha-smooth muscle actin in basal cell epithelioma and its surrounding stroma: with special reference to proliferating cell nuclear antigen expression and adenoid differentiation.

Altered expression of alpha-smooth muscle actin (alpha-SMA) is known to indicate the morphological, tumorigenic and immunological changes occurring in tumour and stromal cells. The purpose of this study was to analyse the dynamics of alpha-SMA expression in human basal cell epithelioma (BCE) cells and their surrounding stromal cells, in the process of differentiation towards cutaneous appendages such as hair, sebaceous, apocrine and eccrine glands. Using anti-alpha-SMA specific monoclonal antibody (MAb), 17 of 36 BCEs (47%) were shown to express alpha-SMA, despite the usual absence of alpha-SMA in all eukaryotic cells except muscle cells. Solid, adenoid and sclerosing types of BCE expressed alpha-SMA more frequently, and in greater amount, than cystic, keratotic and superficial types. Furthermore, the expression of alpha-SMA in BCE cells significantly paralleled the expression of proliferating cell nuclear antigen (PCNA) in these cells. Thus, the altered expression of alpha-SMA may reflect the growing properties of BCE cells under the specific cellular regulations for differentiation. In addition, we have found anti-alpha-SMA MAb-positive fibroblasts with smooth muscle differentiation (myofibroblasts) in desmoplastic stroma surrounding BCE nests in 13 of 36 cases (36%). Coincidental expression of alpha-SMA in both BCE cells and stromal cells was found in nine of the 13 cases (69%), indicating the possibility of the induction of myofibroblastic stromal changes in surrounding tissues by cytokines secreted from BCE cells [e.g. basic fibroblast growth factor (bFGF)-like factor].