AbstractBackgroundConsensus is lacking on adequate deep histological margins in cutaneous squamous cell carcinoma (cSCC). Deep clearance for tumours located on the scalp is limited by anatomic constraints.ObjectiveTo determine whether clear but close deep histological margins (<1 mm) confer a higher risk of recurrence in cSCCs of the scalp treated by wide local excision, compared to deep histological margins ≥1 mm.MethodsMulticentre retrospective observational cohort study and multivariate competing risk analysis to evaluate risk factors for recurrence.ResultsIn total, 295 patients with 338 cSCCs were included. Close deep histological margins were not associated with an increased cumulative incidence of recurrence (subhazard ratio [SHR] 1.96 [95% CI 0.87–4.41]). However, an increased risk of recurrence was observed for those tumours that presented concurrent invasion of the galea aponeurotica and close deep margins, as opposed to patients without these factors (SHR 3.52 [1.24–10.01]). Tumours with clear but close peripheral margins (<1 mm) also had higher risk of recurrence (SHR 5.01 [1.68–14.97]).LimitationsRetrospective observational study based on pathology reports.ConclusionsDeep histological margins <1 mm do not confer a greater risk of recurrence as long as the tumour is completely excised and the galea aponeurotica is not involved. Surgical excision of cSCC on the scalp should include the galea to ensure proper assessment of deep margins.