Solid-pseudopapillary tumor of the pancreas - Immunohistochemical localization of neuroendocrine markers and CD10

To clarify the neuroendocrine differentiation and CD10 expression in solid- pseudopapillary tumors (SPTs) of the pancreas, we performed immunohistochem ical analysis in 19 such tumors, including one solid-pseudopapillary carcin oma (SPC), along with 20 pancreatic neuroendocrine tumors (PNTs), six acina r cell carcinomas (ACCs), and one pancreatoblastoma (PB). We used antisera directed against CD56, synaptophysin, protein gene product 9.5, the alpha-s ubunit of Go protein, chromogranin A, CD10, trypsin, chymotrypsin, various cytokeratins (CKs), CA19-9, vimentin, and alpha-l-antitrypsin (AAT). All SP Ts exhibited immunoreactivity for CD56 and CD10, and 15 expressed other neu roendocrine markers focally with the exception of chromogranin A. Frequent clustering of synaptophysin-positive cells was noted. Two cases contained a peculiar nodule that cytomorphologically and immunohistochemically resembl ed PNT. CD10-positive cells were scarce in one SPC. PNTs were CD56-positive , but often with faint intensity, and staining for other neuroendocrine mar kers, including chromogranin A, was diffusely positive. CD10 was detected, mostly in a focal pattern, in five PNTs. Pan-CK, CK8, CK18, and CK19 were m ore frequently demonstrated in PNT than SPT. Vimentin and AAT were often id entified in PNT as well and were not specific for SPT. ACCs were CD56-negat ive, with the exception of one case designated as a mixed acinar-endocrine carcinoma. PB was focally positive for CD56 at the periphery of the tumor n ests. Four ACCs and one PB exhibited focal CD10 reactivity. This study demo nstrated the unique immunohistochemical features of SPT. Our results also s uggest that SPT exhibits, at least focally, neuroendocrine differentiation, and that these neuroendocrine markers and CD10 are diagnostically useful.