Five-year Recurrence Rate of Cutaneous Squamous Cell Carcinoma After Mohs Micrographic Surgery Versus Standard Excision: a Prospective Multicentre Cohort Study.

BACKGROUND: Mohs micrographic surgery (MMS) is a tissue-sparing alternative for standard excision (SE) for the treatment of cutaneous squamous cell carcinoma (CSCC). Due to its complete margin control, MMS theoretically results in fewer recurrences. However, prospective studies comparing recurrence risk between MMS and SE remain limited, and no randomized controlled trials exist. In clinical practice, MMS tends to be selectively offered for higher-risk tumours, particularly those in cosmetically sensitive areas. OBJECTIVES: To compare 5-year recurrence rates between MMS and SE for primary CSCC, and secondarily to compare metastasis rates and the ratio of final defect size to initial tumour size. METHODS: Prospective multicentre cohort study of patients with primary CSCCs treated with MMS or SE at six centres in the Netherlands. To detect all recurrences, patients were linked to the Dutch Nationwide Pathology Databank. The Fine and Gray competing risk regression model was used to assess the subdistribution hazard ratio (sHR) for recurrence, adjusting for confounders. RESULTS: A total of 761 patients with 903 completely excised primary CSCCs were included: 629 treated with SE and 274 with MMS. Reflecting the selective use of MMS for higher-risk CSCC, tumours treated with MMS were more often classified as high AJCC-8 stage (≥ T2, 55% vs. 25%; p < 0.001), and more frequently located in the H-zone (77% vs. 37%, p < 0.001). The 5-year cumulative incidence of recurrence was 1.7% (95%CI 0.9%-3.0%) for SE and 3.3% (95%CI 1.6%-5.9%) for MMS. After adjustment for AJCC-8 stage, the sHR for recurrence after MMS compared to SE was 1.51 (95% CI, 0.66-3.44; p = 0.33). The 5-year cumulative incidence of metastasis was 0.8% (95%CI 0.3%-1.8%) for SE and 1.1% (0.3%-3.0%) for MMS. The ratio of final defect size to initial tumour size was smaller for MMS (1.2 vs. 3.0, p < 0.001). CONCLUSIONS: No significant difference in 5-year recurrence rate was found between MMS and SE, however, given the non-randomized design and the limited number of events, definitive conclusions about whether a true difference in efficacy exists cannot be drawn. MMS resulted in smaller defects, supporting its use in cosmetically or functionally sensitive areas where tissue preservation is important.