Suggested excisional margins for cutaneous malignant lesions based on Mohs micrographic surgery.

IMPORTANCE Surgical excision of skin cancer is a common treatment, yet the proper surgical margin remains unclear. This study reviews data on lesions and their margins as defined by Mohs micrographic surgery. OBJECTIVE To review margins as defined by Mohs micrographic surgery. DESIGN Retrospective review of data from patients with skin cancer. SETTING Academic medical center. PARTICIPANTS All patients with nonmelanoma skin cancer. MAIN OUTCOME AND MEASURE Size and final defect size were compared to calculate the margins needed. All lesions were categorized based on histologic characteristics. RESULTS A total of 495 lesions were reviewed. All tumors and defects had precise measurements. The mean margins for low-risk basal cell carcinomas, high-risk basal cell carcinomas, low-risk squamous cell carcinomas, and high-risk squamous cell carcinomas were 2.4 mm, 3.7 mm, 2.6 mm, and 5.3 mm, respectively. Statistical differences in surgical margins were found between all low- and high-risk cancer types. Established high-risk zones (H-zone) for basal cell carcinoma and squamous cell carcinoma were not associated with larger margins. Margins required to excise completely 95% of all the low-risk basal cell carcinomas, high-risk basal cell carcinomas, low-risk squamous cell carcinomas, and high-risk squamous cell carcinomas, were 4.75 mm, 8 mm, 5 mm, and 13.25 mm, respectively. CONCLUSIONS AND RELEVANCE Differences are noted between low- and high-risk cutaneous lesions. When primary excision instead of Mohs micrographic surgery is the only option, the aforementioned margins may be considered guidelines. The relevance of this study is to guide future management and margins for primary excision. LEVEL OF EVIDENCE 3.