Galea vs periosteum: impact of excision depth on outcomes for cutaneous squamous cell carcinoma of the scalp

Cutaneous squamous-cell carcinoma (cSCC) is the second most common skin cancer, with local recurrence rates of up to 10% in the scalp. To date there have been no direct comparisons of recurrence rates or deep margin involvement for surgical excision to different anatomical layers of the scalp. A multi-centre retrospective study of all cSCC excised from the scalp from 2015 to 2020 was conducted. Two hundred and seventy nine patients (17-female, 262-male) met the inclusion criteria (median age 82.2 years), incorporating a total of 302 cSCC's. Primary excision depth was galea in 80 cases and periosteum in 222 (26.5% and 73.5% respectively). A significantly greater proportion of lesions excised to galea had involved or close (<1mm) deep margins (n = 27, 33.8% galea vs n = 50, 22.5% periosteum, OR 2.74 [95% CI 1.38-5.45], p = .004). Local recurrence rates were also significantly higher for lesions excised to galea vs periosteum (n = 13, 16.3% vs n = 18, 8.1% respectively, p = .039), although this trend was lost after adjusting for deep margin status. To our knowledge, this study is the first to compare local recurrence rates and margin involvement for cSCC of the scalp excised to different depths. Our findings demonstrate a higher incidence of involved/close deep margins for lesions excised to galea, imposing a higher treatment burden and risk of recurrence for these patients. We therefore advocate including galea in surgical excision.