Histographic surgery: accuracy of visual assessment of the margins of basal-cell epithelioma.

In 72 basal-cell epitheliomas, the clinical extension and the actual extension of the defect measured by complete tumor removal by Mohs' chemosurgery were compared. Subclinical extension depends on the type of basal-cell epithelioma (primary, recurrent), on case history, location, clinical diameter, number of previous treatments and histological type. It is remarkably great in large (diameter more than 20 mm), in morphea-like basal-cell epitheliomas on the forehead, temple and scalp, especially following several previous treatments. In such cases the excision should include at least a 5-10 mm margin of "normal tissue." Present results again show that "histographic," that is, Mohs' chemosurgery is the method of choice for the treatment for these tumors.