Basal cell carcinomas (BCCs) with high-risk features are preferably treated by Mohs micrographic surgery. Studies have shown clinicopathologic characteristics that may predict more stages required for clearance. However, few studies have correlated such factors with the number of millimeters removed per stage.

To determine margins necessary for BCC clearance according to tumor features, especially for tumors less than 6 mm, and to suggest initial margins for Mohs micrographic surgery and margins for wide local excision.

Retrospective analysis of 295 consecutive Mohs micrographic surgeries for primary BCCs. Variables analyzed included patient age, sex, immunostatus, lesion size, location, histologic subtype, borders, stage number, and millimeters excised per stage.

BCCs less than 6 mm had a clearance rate of 96% with 3-mm margins. In adjusted multivariable analysis, superficial, micronodular, infiltrative, and morpheaform subtypes were associated with larger margins, whereas clinically well-defined tumors were associated with smaller margins.

Because of the limited sample of certain subtypes, a 3-mm margin is better suited for nodular tumors.

These data help guide initial Mohs micrographic surgery and wide local excision margins required for tumor clearance according to tumor features. Nodular BCCs less than 6 mm may be cleared with 3-mm margins instead of the current 4-mm margin recommendation.