Stromal expression of actin is a marker of aggressiveness in basal cell carcinoma

Basal cell carcinoma is a very common malignant skin tumor that rarely metastasizes but is often locally aggressive. In a number of studies conducted by different investigators, Bcl2, beta-catenin, cyclin D1, hMSH2, and alpha-smooth muscle actin have been reported to have potential for predicting basal cell carcinoma aggressiveness. However, these reports were inconclusive and sometimes contradictory. We therefore studied the expression and topographic locations (tumor versus stroma) of all these gene products in a group of clinically proven aggressive basal cell carcinomas (n = 30) and randomly selected control cases of nonaggressive basal cell carcinomas (n = 33). The results were subjected to statistical analysis with Mann-Whitney test and logistic regression. The accuracy of the resulting significant discriminating criteria was further tested using the omnibus tests of model coefficients. With multivariate analysis, differential expression of Bcl-2, beta-catenin, and cyclin D1 was not significantly different between aggressive and nonaggressive tumors. hMSH2 expression was up-regulated in the aggressive tumors (P = .005). Alpha-smooth muscle actin was expressed by tumor cells in both study groups, but stromal expression of alpha-smooth muscle actin was restricted to the aggressive tumors and highly predictive of aggressive behavior (P < .001; accuracy, 87%). Logistic regression combining the expression of alpha-smooth muscle actin and hMSH2 yielded a predictive model with 97% accuracy (P < .001). These data show conclusively that aggressive basal cell carcinomas express alpha-smooth muscle actin in the stroma, whereas nonaggressive basal cell carcinomas express alpha-smooth muscle actin in the tumor cells, and that stromal expression of alpha-smooth muscle actin is an accurate, reliable, and easy to use marker of aggressiveness in basal cell carcinomas and can be used in clinical practice for surgical therapeutic decisions.