Solid and papillary epithelial neoplasm arising in heterotopic pancreatic tissue of the mesocolon

Aim-Solid and papillary epithelial neoplasm (SPEN) is an uncommon pancreati c tumour. Very rarely it has also been described outside the pancreas, usua lly arising from heterotopic pancreatic tissue. This report summarises all the published extrapancreatic SPENs and documents the sixth such case arisi ng from heterotopic pancreatic tissue of the transverse mesocolon in a 15 y ear old girl. Methods/Results-Histological and immunohistochemical examination revealed t ypical papillary and solid areas composed of columnar, cuboidal, and round cells, which were focally positive for vimentin, cytokeratin, neurone speci fic enolase, carcinoembryonic antigen, alpha1-antitrypsin, alpha1-antichymo trypsin, and negative for neuroendocrine markers (neurofilament, PGP 9.5, c hromogranin A, synaptophysin, and S100), p53, and oestrogen and progesteron e receptors. Electron microscopy showed scant zymogen but no neurosecretory granules. In agreement with the flow cytometric result of diploidy, compar ative genomic hybridisation (CGH) did not reveal loss or gain of genetic ma terial, and the in situ hybridisation analysis of the RB1 and p53 genes rev ealed no abnormality in the 13q and 17p arms. Conclusions-Immunohistochemical and electron microscopic data support exocr ine differentiation. The CGH and the flow cytometric results suggest a subt le, yet unknown genetic change, rather than a large genetic alteration. RB1 and p53 in situ hybridisation ruled out the role of deletion at these site s in the pathogenesis of SPEN. Interestingly, review of the published and t he present heterotopic pancreatic SPENs identified the mesocolon as the mos t common anatomical site (four of six), despite the very rare occurrence of ectopic pancreatic tissue at this site.