Mohs Micrographic Surgery for Basal Cell Carcinoma: Predictive Factors for Increased Stages and Relative Defect Sizes

Keratinocyte cancers (KCs), including basal cell carcinomas (BCCs), are the most common cancers in Australia. While Mohs micrographic surgery (MMS) is the gold standard treatment, it can be resource intensive, particularly for cases requiring multiple stages. This study aimed to identify predictors of increased MMS stages and a greater tumour-to-defect size discrepancy in head and neck BCC. A retrospective analysis of the Mohs Electronic Database at the Skin Hospital's Westmead and Darlinghurst sites in Sydney, Australia was conducted from October 2012 to December 2022, including 18,346 BCC cases. The main outcomes were the number of MMS stages and the relative defect size, with covariates including patient age, sex, tumour characteristics and Mohs specialist factors. Older patients required more stages (1.65 vs. 1.90; p < 0.01) and had larger relative defect sizes (2.10 vs. 2.90; p < 0.01). Larger tumours required more stages (1.69 vs. 1.94; p < 0.01), while smaller tumours had disproportionately larger relative defects (5.94 vs. 2.08; p < 0.01). Nodular BCC required fewer stages (1.63; p < 0.01) and had the smallest defects (2.11; p < 0.01). Notably, superficial BCCs required a similar number of MMS stages as traditionally aggressive subtypes. Tumours of the ear, eye and nose required more stages than other cosmetic units (2.05, 2.02, 1.94; p < 0.01). Increased Mohs experience reduced the number of stages (2.18 vs. 1.83; p = 0.03) and relative defect sizes (3.49 vs. 2.50; p < 0.01). Patient age, tumour size, subtype, cosmetic unit and Mohs specialist experience influence MMS stages and relative defect sizes in head and neck BCC. Recognising these factors can enhance surgical planning, personalise treatment strategies and improve patient outcomes.