Primary low-grade neuroendocrine carcinoma of the skin: An exceedingly rare entity.

Low-grade neuroendocrine tumors (NETs), also known as carcinoid tumor, commonly arise from the gastrointestinal (GI) and pulmonary tracts, but rarely occur in the skin. Cutaneous NET typically occurs as metastases or high-grade primary lesions, called Merkel cell carcinoma. In the few cases described in literature, primary low-grade neuroendocrine carcinomas of the skin (LGNECS) are usually indolent cutaneous nodules, presenting on the head and trunk of elderly patients. LGNECS tumors are histologically similar to its counterparts arising in other anatomic locations. As there is no NET cut-off for the skin due to their rarity, the GI scale was used instead; low-grade NETs have a Ki-67 proliferative index of less than 3%. The distinction between primary and metastatic NET, however, is not absolute and can be difficult. A primary vs metastatic NET diagnosis relies on clinical exclusion of a NET in other, more common, anatomic locations. Here, we present a case of an LGNECS on the scalp of a 72-year-old female patient. Whole body imaging failed to identify any octreotide-avid lesions elsewhere in the patient, aside from 2 positive cervical lymph nodes, which were confirmed with a node dissection and histologic evaluation. This is the 19th reported case of LGNECS and the 2nd reported case of LGNECS with nodal metastasis.