CDX2 and neuroendocrine neoplasm: Immunostaining techniques were employed in this case to further evaluate the discovered malignancy and revealed the tumor stained negative for TTF-1 and positively stained for CD56, chromogranin A, synaptophysin, pan keratin (AE1/AE3), and CDX2; this pattern of immunohistochemistry staining indicated that this is likely a primary neuroendocrine tumor of the GI tract, most likely originating from the foregut or midgut [13].