Subclinical Extension of Pigmented Nodular Type Basal Cell Carcinoma in Japanese Patients.

Background: In Japan, resection of basal cell carcinoma (BCC) with a margin of at least 4 mm is recommended by guidelines. Objectives: This study aimed to investigate the effectiveness of surgical margins for well-defined pigmented BCC in Japanese patients. Methods: Between 2010 and 2017, 25 cases of well-defined nodular pigmented BCC measuring 20 mm or less on the face were surgically resected with a margin of 4 to 5 mm, and pathological measurements were performed at the National Hospital Organization Nagasaki Medical Center. The measurement item was subclinical extension of the tumor, which is the difference in distance between the actual tumor border confirmed under a microscope and apparent tumor border determined clinically from the outside. Results: Subclinical extension of the tumors ranged from 0 to 3.5 mm, with a mean of 1.0 mm, standard deviation of 1.0 mm, and 95% confidence interval of 0.7 to 1.6 mm. Regardless of the malignancy grade, resection with a 3-mm margin for nodular pigmented BCC with a clear border and long diameter of 20 mm or less was effective, with a complete resection rate of 96%. Conclusions: Surgical excision with a 3-mm margin is reliable treatment for well-defined, primary pigmented BCC, with a complete removal rate of 96%. These results suggest that resection margins recommended in guidelines can be narrowed in Japanese patients with BCC.