Predictors of extensive subclinical spread in nonmelanoma skin cancer treated with Mohs micrographic surgery

Background: In nonmelanoma skin cancer, the clinically visible portion may represent a small fraction of microscopic tumor spread. Previous studies have examined individual risk factors for subclinical spread based on patient and tumor characteristics. However, these risk factors have not been prioritized or studied in combination. Objective: To identify the most predictive risk factors for extensive subclinical tumor spread. Design: Retrospective analysis of 1131 Mohs micrographic surgical cases. Variables analyzed included patient age, sex, and immune status and lesion size, location, histologic subtype, and recurrence. Logistic regression was applied to identify important combinations of tumor characteristics and to quantify relative odds of spread. Setting: Academic referral center. Patients: Consecutive sample of all referred patients treated by a single Mobs micrographic surgeon in a 3-year period. Main Outcome Measure: Number of Mohs micrographic surgical layers required to clear a tumor, with 3 or more layers defined as extensive subclinical spread. Results: The highest-risk tumors, with odds ratios greater than 6.0, were basosquamous and morpheaform basal cell carcinoma (BCC) on the nose, morpheaform BCC on the cheek, and those with a preoperative size greater than 25 mm. Other important risk factors were recurrent and nodular BCC on the nose; location on the eyelid, temple, or ear helix; neck tumors and recurrent BCC in men; and tumor size greater than 10 mm. Patients younger than 35 years were at lower risk. Increasing age and immunocompromise were not significant predictors. Conclusion: Identification of lesions likely to exhibit extensive subclinical spread an help guide management to ensure complete tumor eradication and thereby reduce the risk of recurrence and its associated morbidity and cost.