Risk Factors for Microscopic Margin Positivity in Basal Cell Carcinoma Excision With a 2‐mm Surgical Margin: A Japanese Retrospective Study

Basal cell carcinoma is a common locally invasive and destructive skin cancer, if inadequately treated. Although topical noninvasive treatment has been reported, surgical excision is currently the gold standard. Surgical excision is performed with a predetermined surgical margin. There is worldwide debate on the optimal margin. Some guidelines recommend surgical margins > 4 mm; however, Asians reports suggest a narrow surgical margin may be suitable. We previously reported that a 2-mm margin is acceptable for specific tumors. We aimed to clarify whether a 2-mm margin is suitable for all lesions and the differences in local recurrence between surgical procedures (one-step or two-step surgery). We retrospectively reviewed the data of 112 patients who underwent surgical excision with predetermined 2-mm or > 2-mm margins. Pathological reports and surgical procedure databases were collected and statistically analyzed to clarify topical factors for microscopic margin clearance. We compared differences between macroscopic peripheral margins and the distance of microscopic margins and analyzed associations between surgical procedure and local recurrence. Aggressive type was significantly associated with poorly-defined borders (p < 0.01), and microscopic excisional margin positivity was correlated with tumor thickness (p < 0.01). The correlation coefficient between tumor size and tumor thickness was 0.321 and the p-value was 0.0005, indicating a weak correlation between a larger tumor size and a greater tumor thickness. The macroscopic surgical margin was significantly associated with the microscopic peripheral margin (p < 0.001). Tumor size was significantly associated with tumor thickness, and aggressive type tumors were significantly poorly defined. Additionally, tumor size, tumor thickness, and tumor subtype aggressiveness were the strongest risk factors for microscopic margin positivity. For adequate treatment, poorly defined tumors, wider tumors, and aggressive tumor types were carefully treated, and confirmation after excision with a 2-mm margin by two-step surgery or accompanied with frozen section estimation. For well-pigmented and well-defined basal cell carcinomas, a 2-mm margin may be more suitable than for the two types requiring careful treatment.