P189 Shallow cuts, deeper issues: the primacy of deep margins in cutaneous squamous cell cancer

Abstract

Cutaneous squamous cell carcinoma (cSCC) is a major public health concern in the UK. Surgical excision remains the mainstay of treatment. The BAD guidelines specify peripheral excision margins according to risk category, but offer limited guidance on deep margins, despite frequent incomplete excision at this plane. Adherence to peripheral margin recommendations is variable, partly because many risk factors are identified only histologically. We aimed to assess adherence to BAD excision margin guidelines in high- and very high-risk cSCC, to explore reasons for nonadherence, and evaluate the impact of adherence on histological margin status. A retrospective review was conducted of 149 consecutive high- and very high-risk cSCCs excised between January 2023 and January 2025 at a single centre. Lesions with incomplete histology, nodal or visceral metastases, or wedge excisions were excluded. Demographic, surgical and histological data were extracted and independently verified. Descriptive statistics were applied. In total 144 lesions met the inclusion criteria (37 high risk, 107 very high risk). The mean tumour diameter was 26.6 mm and the mean thickness 5.3 mm. Only 30.8% of very high-risk lesions (33 of 107) were defined preoperatively. Complete histological excision was achieved in 118 of the 144 cases (81.9%): 100% of high-risk and 75.7% of very high-risk tumours. Among incompletely or narrowly excised tumours, 97% involved the deep plane. Peripheral margin involvement was uncommon. Correctly marked peripheral margins in accordance with BAD guidance occurred in 18% of cases, yet complete excision rates were similar regardless of adherence (75% with or without adherence). Nonadherence to BAD excision margins largely reflects histological upstaging rather than surgical error. Incomplete excision predominantly occurs at the deep plane. Greater focus on strategies to optimize deep margin clearance may improve outcomes for cSCCs. Current guidelines underemphasize deep surgical planning; the need for experienced clinician members of the appropriate skin cancer multidisciplinary team is even more crucial.