Cutaneous squamous cell carcinoma carries a low but significant risk of metastasis and death. In this study, patients with CSCC had a 3.7% risk of metastasis and 2.1% risk of disease-specific death. Tumor diameter of at least 2 cm, invasion beyond fat, poor differentiation, perineural invasion, and ear, temple, or anogenital location were risk factors associated with poor outcomes. Accurate risk estimation of outcomes from population-based data and clinical trials proving the utility of disease-staging modalities and adjuvant therapy is needed.

CTCL is a cancer of skin homing T cells with variants that include leukemic CTCL (L-CTCL), a malignancy of central memory T cells (TCM), and mycosis fungoides (MF), a malignancy of skin resident effector memory T cells (TEM). We report that low-dose alemtuzumab (αCD52) effectively treated patients with refractory L-CTCL but not MF. Alemtuzumab depleted all T cells in blood and depleted both benign and malignant TCM from skin, but a diverse population of skin resident TEM remained in skin after therapy. T-cell depletion with alemtuzumab required the presence of neutrophils, a cell type frequent in blood but rare in normal skin. These data suggest that TCM were depleted because they recirculate between the blood and skin whereas skin resident TEM were spared because they are sessile and non-recirculating. After alemtuzumab treatment, skin T cells produced lower amounts of IL-4 and higher amounts of IFNγ. Moreover, there was a marked lack of infections in alemtuzumab-treated L-CTCL patients despite the complete absence of T cells in blood, suggesting that skin resident TEM can protect the skin from pathogens even in the absence of T cell recruitment from the circulation. Together, these data suggest that alemtuzumab may treat refractory L-CTCL without severely compromising the immune response to infection by depleting circulating TCM but sparing the skin resident TEM that provide local immune protection of the skin.

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Squamous cell carcinoma involving unnamed small nerves (<0.1 mm in caliber) may have a low risk of poor outcomes in the absence of other risk factors. Large-caliber nerve invasion is associated with an elevated risk of nodal metastasis and death, but this is due in part to multiple other risk factors associated with large-caliber nerve invasion. A larger study is needed to estimate the specific prognostic impact of nerve caliber.