Insulinoma‐associated 1: A novel nuclear marker in Merkel cell carcinoma (cutaneous neuroendocrine carcinoma)

• Published in: Journal of cutaneous pathology Vol. 45; no. 2; pp. 129 - 135
• Main Authors: Rush, Patrick S., Rosenbaum, Jason N., Roy, Madhuchhanda, Baus, Rebecca M., Bennett, Daniel D., Lloyd, Ricardo V.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.02.2018; Wiley Subscription Services, Inc
• Subjects: Basal cell carcinoma; carcinoma; Cell cycle; cutaneous neuroendocrine; Differential diagnosis; Ewing's sarcoma; Immunohistochemistry; immunoperoxidase; INSM1; Insulinoma; Melanoma; Merkel cell; Metastases; Neoplasia; neuroendocrine; Neuroendocrine tumors; Tumor cells; Tumors; immunoperoxidase; neuroendocrine; INSM1; carcinoma; cutaneous neuroendocrine; Merkel cell
• ISSN: 0303-6987; 1600-0560
• DOI: 10.1111/cup.13079

Merkel cell carcinoma (MCC) is a rare, clinically aggressive, cutaneous neuroendocrine (NE) neoplasm. As a tumor with small, round, blue cells, the histologic differential diagnosis for MCC can include melanoma, metastatic small cell carcinoma (SCC), nodular hematopoietic tumors, basal cell carcinoma (BCC), atypical variants of squamous carcinoma and the uncommon occurrence of primary cutaneous Ewing sarcoma. In cases with atypical histology or without the classic immunophenotype, the diagnosis can be challenging. Ultimately, immunohistochemistry (IHC) is essential to the definitive diagnosis of MCC and in difficult cases, the diagnosis may hinge entirely on the immunophenotype of the tumor cells. Insulinoma‐associated 1 (INSM1) is a transcription factor expressed in tissues undergoing terminal NE differentiation. As a nuclear protein tied to both differentiation and the cell cycle, INSM1 may offer additional utility in comparison to traditional, cytoplasmic markers of NE differentiation.