Different beta-catenin immunoexpression in carcinoid tumors of the appendix in comparison to other gastrointestinal carcinoid tumors.

Carcinoid tumor of the appendix is an endocrine tumor that is histologically similar to, but biologically less aggressive than carcinoids arising from other parts of the gastrointestinal tract. In this study, we examined E-cadherin, beta-catenin, DCC, p53 and Ki67 immunoexpression in cases of carcinoid of the appendix and made a comparison with non-appendiceal carcinoid tumors. Nine cases of appendiceal carcinoid and 11 biopsies of carcinoid of other parts of the gastrointestinal tract, five cases of the small intestine and six of the stomach were immunohistochemically evaluated for Ki67, p53, DCC, E-cadherin and beta-catenin. Two main patterns of beta-catenin staining were observed. The first pattern was characterized as membranous and cytoplasmic, and was seen mainly in the peripheral cells of the nests. The second pattern was diffuse, predominantly membranous. Most (five of seven) appendiceal carcinoids and only three of 11 non-appendiceal cases showed the first staining pattern (p < 0.05). Immunoexpression of E-cadherin and DCC was similar in both groups. p53 and Ki-67 immunostaining revealed stronger nuclear positivity in the non-appendiceal carcinoid tumors (statistically not significant). We found a pattern of beta-catenin immunostaining in typical carcinoid tumors of the appendix that was different from the pattern seen in non-appendiceal carcinoid tumors. This alteration suggests that carcinoid of the appendix may represent a different subtype of carcinoid tumors with different immunohistochemical and biological behavior.