Metastatic Malignant Melanoma With Neuroendocrine Differentiation

A Case Report and Review of the Literature

Carl Christofer Juhlin; Jan Zedenius; Felix Haglund


J Med Case Reports. 2020;14(44) 

In This Article


The distinction between a neuroendocrine tumor (NET) and various epithelial and non-epithelial tumors with focal neuroendocrine differentiation is an established clinical dilemma. The diagnosis relies on the identification of clear-cut immunoreactivity towards neuroendocrine markers such as chromogranin A (CgA), synaptophysin (SYP), and CD56, but the expression of one or several of these markers might also be found in subsets of non-NETs.[1–6] As these tumors are biologically distinct from NETs, the associated treatment options vary; therefore, proper recognition is imperative for the patient's overall prognosis. The distinction between a metastatic NET and non-NET tumor with focal neuroendocrine differentiation could be particularly difficult when assessing biopsy material of metastatic deposits from a cancer of unknown primary (CUP), given the general privation of tissue material for immunohistochemical purposes.

CgA and SYP are proteins associated with vesicles of neurons and endocrine cells, with established roles for the secretion of various peptides mediated through exocytosis.[7,8] NETs are usually positive for both markers, reflecting the underlying secretory potential of these tumor types. CD56, also known as neural cell adhesion molecule (NCAM), is important for inducing neurite outgrowth in neurons, but is also generally present in NETs.[9] Not surprisingly, non-NET carcinomas might also express CgA, SYP, and/or CD56 to a variable extent. This phenomenon is well described for a variety of tumor types – and sometimes also coupled to specific clinical characteristics and patient prognosis. For example, prostatic adenocarcinoma with focal neuroendocrine differentiation is associated with worse clinical outcome, whereas the same correlation is not found in adenocarcinomas of the breast.[2,3]

In this case report, we describe a patient with disseminated metastatic disease and depict how the manifestation of a malignant melanoma with neuroendocrine features mimicked a neuroendocrine carcinoma (NEC) from histological and immunophenotypic aspects, including the clinical consequences.