SYP and skin squamous cell carcinoma: Harms et al. studied seven cases of intraepidermal MCC-associated cSCC in situ with a dermal MCC component, and demonstrated that cSCC in situ associated with MCC exhibited upregulation of both epidermal markers, such as KRT6A and KRT6B, and intermediate levels of neuroendocrine markers like SYP and DACH1, implying clonal relatedness between virus-negative MCC and associated cSCC in situ (ref. [41]).