Scalp at High Risk for Cutaneous Squamous Cell Carcinoma Metastasis

The scalp is a high-risk area for cutaneous squamous cell carcinoma (cSCC) metastasis, similar to the lip and ear, study data published in the Journal of the American Academy of Dermatology demonstrated. These results may guide clinicians in the treatment of patients with cSCC on the scalp.

Current National Comprehensive Cancer Network guidelines describe the lip and ear as high-risk regions for cSCC metastasis and the scalp as a moderate risk region. Investigators sought to quantify the metastatic risk for cSCC on the scalp vs lip or ear.

Patients who underwent Mohs micrographic surgery between September 1, 2005 and September 1, 2019 at the Hospital of the University of Pennsylvania for invasive cSCC on the lip, ear, scalp, or pretibial leg were eligible for inclusion. Only patients with cSCC of at least 2 cm in diameter were included in the study. Linear and Poisson regression were used to identify risk factors for metastasis. Models were adjusted for intra-patient correlation using clustered standard errors. The pretibial leg was used as a low-risk reference site; lip and ear were considered high-risk sites.

Data from 432 cSCC were analyzed: 15 (3.5%) on the lip; 72 (16.9%) on the ear; 198 (45.8%) on the scalp; and 146 (33.8%) on the pretibial leg. The scalp, ear, and lip groups did not significantly differ by tumor diameter, median follow-up time, depth of invasion, or degree of differentiation. Patients with cSCC on the pretibial leg had slightly longer follow-up times compared with the ear (P =.03) and scalp (P =.005) groups; lower incidence of perineural invasion compared with the ear (P =.005); and shallower depth of invasion compared with the ear (P <.001), scalp (P <.001), and lip (P =.04).

Scalp cSCCs had significantly higher rates of metastasis compared with pretibial leg cSCCs (9.1% vs 0%; P =.002). Lip and ear cSCCs also had significantly higher metastasis rates than pretibial leg cSCCs (9.1% vs 0%; P =.003). After controlling for depth of invasion, sex, age, and immunocompromised status, the rate of metastasis was not significantly different between the scalp and the ear or lip (9.09% vs 9.09%; P =.99).

In multivariate regression models, location on the scalp was an independent risk factor for metastasis. Immunocompromised status was independently associated with metastatic risk for cSCC on the ear or lip (risk ratio, 6.02; 95% CI, 1.3-28.6), although not for cSCC on the scalp.

The small sample size prevented evaluation of risk by anatomic depth of invasion on the scalp, it was noted.

These results demonstrated to the investigators that cSCCs on the scalp are at high risk for metastasis, particularly compared with the pretibial leg. Further study is necessary to identify other risk factors for metastasis on the scalp.

Reference

Mo J, Miller CJ, Karakousis G, Keele K, CohenJ, Krouse RS. The scalp is a high-risk site for cutaneous squamous cell carcinoma metastasis. Published online September 17, 2020. J Am Acad Dermatol. doi: 10.1016/j.jaad.2020.09.035