Positive INSM1 and synaptophysin immunostaining indicated neuroendocrine differentiation, ruling out the diagnosis of colorectal adenocarcinoma.13 Negative chromogranin staining, a classic marker for neuroendocrine cells that is less consistently positive in neuroendocrine carcinoma, was observed in the present patient. Here, INSM1 is linked to neuroendocrine carcinoma.