Tubular carcinoids of the appendix: The CK7/CK20 immunophenotype can be a diagnostic pitfall

Aims: Tubular carcinoid is a rare variant of appendiceal well-differentiated neuroendocrine tumour. Although considered benign lesions, the small infiltrating tubules that characterise the tumour may raise concern for metastatic adenocarcinoma. To our knowledge, the cytokeratin 7 (CK7)/cytokeratin 20 (CK20) expression profile of these neoplasms remains unexplored. Methods: The authors characterised the CK7/CK20 immunophenotype and Ki-67 expression of the eight available tubular carcinoids seen at their institution from 1991 to 2011. Results: CK7 and CK20 staining was variable, ranging from none to focal staining for either or both CK7 and CK20, to diffuse expression of CK7 or CK20. Conclusions: The CK7/CK20 expression profile is of limited value when the differential diagnosis includes primary tubular carcinoid and well-differentiated metastatic adenocarcinoma. In such cases, careful attention to the location of the neoplasm, mitotic count and presence or absence of an associated classic carcinoid component are more useful for arriving at the correct diagnosis.