Prediction of subclinical tumor infiltration in basal cell carcinoma.

Two thousand-sixteen basal cell carcinomas (BCCs) were documented in terms of age, anatomic location, tumor diameter, initial excision depth, safety margin, histologic type, and the position of tumor outgrowths as determined by three-dimensional histologic study of the tumor margins in paraffin sections (micrographic surgery). The extent of each subsequent excision was recorded until tumor-free tissue was reached. The results showed that BCCs have a highly irregular infiltration pattern and a predilection for small, fingerlike outgrowths whose bases occupy 1-30 degrees of the tumor circumference. When superficial extension was expressed mathematically, the resulting exponential functions varied highly significantly (P = .001) according to histologic tumor type and diameter. The resulting curves permitted very precise prediction of the probability of tumor-positive margins (ie, subtotal excision), depending on the safety margin, histologic tumor type, and tumor diameter. For example, the probability of tumor-positive margins after excision of a BCC up to 10 mm in diameter is 30% with a safety margin of 2 mm, 16% with a safety margin of 3 mm, and 5% with a safety margin of 5 mm. The probability of tumor-positive margins for fibrosing primary BCCs 10-20 mm in diameter is 48, 34, and 18% with safety margins of 2, 3, and 5 mm, respectively. Recurrent tumors have a significantly higher probability of positive margins (P = .001) than primary ones. Anatomic location and tumor age affect subclinical extension only indirectly.