Tissue-sparing properties of Mohs micrographic surgery for infiltrative basal cell carcinoma

Mohs micrographic surgery (MMS) should lead to tissue sparing of healthy skin compared with standard surgical excision because smaller surgical margins are used. To quantify the tissue-sparing properties of MMS in primary basal cell carcinoma (BCC) with an infiltrative growth pattern. A prospective study including 256 primary BCCs with an infiltrative growth pattern was performed. Tumor sizes were measured in 2 perpendicular directions. Surface defect areas after MMS were measured. The suspected defect surface area with standard excision using a 5-mm margin was calculated. The primary outcome of this study was the size of the defect surface area spared with MMS compared with the calculated defect surface area with a standard excision. The median tumor size was 71 mm2, and the median defect size after MMS was 154 mm2. The median defect size calculated for standard surgical excision was 298 mm2. We have shown that MMS of BCC with an infiltrative growth pattern had a 46.4% tissue-sparing effect when compared with standard surgical excision (95% confidence interval, 43.4%-49.1%; P value