Skin neuroendocrine neoplasms

A uniform classification system has been proposed for all neuroendocrine neoplasms, despite organ-specific differences, with the intent to allow pathologists and clinicians to manage their patients with NENs consistently, and to facilitate comparisons between the different entities falling into this category of neoplasms. The new World Health Organization (WHO) 2019 of the skin tumors recognized only two well-established entities: (1) Merkel cell carcinoma (MCC) and (2) endocrine mucin-producing sweat gland carcinoma (EMPSGC). The prototypical primary skin NEN is MCC that it is a high-grade neuroendocrine carcinoma. The endocrine mucin-producing sweat gland carcinoma and skin neuroendocrine tumor represent instead the low-intermediate grade of neuroendocrine skin tumors. To date all skin NENs are exceedingly rare, precluding the need for a common classification of skin neuroendocrine neoplasm. Here we present a realistic and practical formulation for skin NENs based on clinico-pathological and molecular data with the goal to manage these tumors in the most uniform way possible.