Episodic progression and regression of basal cell carcinomas.

Metabolic activity and structure of the stroma adjacent to basel cell carcinomas are closely related to cytological aspects and proliferative activity of the neoplastic cells. Basal cell carcinomas without clear evidence for regression compress or infiltrate an apparently normal dermis where cellular replication is low. Conversely regressing zones of basal cell carcinomas are surrounded by a remodelled stroma where fibroblasts and endothelial cells show signs of proliferation. When regression affects the palisaded array of cells, clefts occur between the basal cell carcinoma and the adjacent stroma. Progression of most types of basal carcinomas may proceed by successive extension and partial regression. More than one type of stroma reaction may be present ina single basal cell carcinoma and the overall pattern may be regarded as the result of successive phases of growth and regression of the neoplasm.