Poorly differentiated cutaneous squamous cell carcinomas have high incomplete excision rates with UK minimum recommended pre-determined surgical margins.

Background: In the UK, the British Association of Dermatology-British Association of Plastic, Reconstructive and Aesthetic Surgery (BAD-BAPRAS) guidelines recommend excision of high-risk cutaneous squamous cell carcinomas (cSCCs), including poorly differentiated cSCCs, with a minimum peripheral margin of 6 mm.

Objectives: We assess whether the BAD-BAPRAS minimum margin achieves histological clearance in poorly differentiated cSCCs.

Patients And Methods: Demographics, surgical notes and histological reports from all patients having a primary cSCC excised at the Plastic Surgery Department of Addenbrooke's Hospital, Cambridge, UK, between January 2017 and April 2018 were analysed. Ordinal regression was performed for excision margin status versus histological grade by using size and site as co-variates.

Results: Of 296 cSCCs, 38(12.8%) were poorly differentiated. Patients with poorly differentiated cSCCs were older (81.1 years vs. 76.7 years, p = 0.038), had lesions on the face or scalp (89.2% vs. 52.1%, p = 0.0001), and had lymphovascular (10.5% vs. 0%, p = 0.001) or perineural invasion (15.8% vs. 2%, p = 0.002). Well-differentiated cSCCs were excised with an average peripheral margin of 4.72 mm (95% CI 4.25-5.18 mm), while poorly differentiated cSCCs were excised with a margin of 6.42 mm(95% CI 5.58-7.28 mm). Close or involved peripheral margins were seen in 3% of well-differentiated lesions but in 13.2% of poorly differentiated lesions (OR=45.02; p = 0.003). Deep margins were close in 13.1% (none involved) of well-differentiated lesions but close or involved in 50% of poorly differentiated lesions (OR=11.94; p = 0.001).

Conclusions: We demonstrate that poorly differentiated cSCCs are frequently incompletely excised in both peripheral and deep planes, despite adherence to guidelines. The UK BAD-BAPRAS guidelines should be urgently updated in line with international consensus.