Skin Metastases of Gastrointestinal Neuroendocrine Tumors - Literature Review.

<b> Introduction:</b> Gastrointestinal neuroendocrine neoplasms arise from cells of the diffuse endocrine system (DES) located in the digestive tract. They are often diagnosed in an advanced stage, when distant metastases appear. Skin metastases of neuroendocrine tumors are extremely rare. </br></br> <b>Aim:</b> The aim of the study was to collect and analyze cases of skin metastases of gastrointestinal neuroendocrine neoplasms. </br></br> <b>Materials and methods:</b> A literature search across PubMed and Medline databases from 1969 up to 2021 was performed. We reviewed English literature according to the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines. The following keywords were used: "neuroendocrine tumor", "neuroendocrine neoplasm", "neuroendocrine carcinoma", "NET", "NEN", "skin and cutaneous metastases", "lymph nodes". The characteristics of patients, grading, tumor localization and other data that was found in publications were assessed. Case reports and case series were included. </br></br> <b>Results:</b> The initial search strategy yielded 14 results in PubMed and 3 in the Medline database. We removed duplicates after we imported the citations with a citation manager. We found 17 publications concerning skin metastases of neuroendocrine neoplasms. The analysis of 18 cases concerned 13 NECs and 5 NETs. In most cases, the metastases are small, painless and located on the scalp or lower extremities. Skin metastases may be the first symptom of the disease. The pancreas is the most common primary tumor site.</br></br> <b>Conclusions:</b> NEN metastases to the skin are often diagnosed with disseminated neoplastic process, which is associated with poor prognosis and high mortality. NET metastases to the skin may occur with an unknown primary site. Skin metastases of neuroendocrine tumors should be considered during the diagnosis of skin tumors.