Insulinoma-associated protein 1 (INSM1), a zinc-finger transcription factor, is a key regulator of neuroendocrine differentiation during development, and has recently emerged as a reliable immunostaining marker with a nuclear staining pattern for the identification of neuroendocrine and neuroepithelial neoplasms.15,16 Several studies have demonstrated nuclear INSM1 expression in multiple neuroendocrine tumor types, including small cell carcinomas […]