Normal intestinal endocrine cells are positive for chromogranin A (CgA) and synaptophysin (SPY) immunohistochemical staining, which are the most commonly used markers for neuroendocrine cells and their tumors. CgA is co-stored and co-secreted with catecholamine in carcinoids.

CgA and SPY immunostaining was performed with forty intestinal carcinoids, consisting of 4 duodenal, 14 ileal, 5 appendiceal and 17 colorectal carcinoids.

Duodenal and ileal carcinoids were strongly positive for CgA, with or without invasion through intestinal wall. Small appendiceal carcinoids were weakly immunostained for CgA and SPY. Colorectal carcinoids were low-grade tumors especially those of small polypoid tumors (< 1.0 cm) with CgA-negative staining while larger tumors (> 2.0 cm) infiltrating through wall were more aggressive with often CgA positive staining. CgA positive carcinoids of duodenum, small intestine and colorectum of larger than 2 cm are more aggressive than CgA negative colorectal tumors, majority of the latter was less than 2 cm. Midgut carcinoids of duodenal, ileal and ascending colon are strongly positive for CgA associated with high serum CgA levels while hindgut carcinoids of rectum, those of small polypoid tumors are negative for CgA but positive for SPY immunostaining.

Thus, CgA-positive immunostaining may be used as an independent marker for potential malignancy for gastroenteropancreatic neuroendocrine tumors regarding the location and sizes of tumors. Some colorectal carcinoids were negative for CgA but were all positive for SPY while some foregut carcinoids with positive CgA staining were negative for SPY immunostaining. Thus, CgA and SPY immunostaining provides significant information in carcinoids.