Paranuclear dot-like immunostaining for CD99: presence in colonic adenomas and adenocarcinomas

Utility of CD99 Paranuclear Expression in the Differential Diagnosis of Merkel Cell Carcinoma

BACKGROUND

Recent reviews have referred to the paranuclear dot-like staining pattern of CD99 in several neoplasms, including solid pseudopapillary tumors in the pancreas, colonic adenocarcinomas, and colonic adenomas as well as in Merkel cell carcinoma (MCC). The aim of this work was to explore the utility of CD99 paranuclear staining in the differential diagnosis of MCC.

MATERIAL AND METHODS

We explore paranuclear dot-like CD99 expression in several small, round blue cell neoplasms, including neuroendocrine neoplasms, Ewing sarcomas/primitive neuroectodermal tumors (EWS/PNET), melanomas, small cell lung carcinomas (SCC), lymphoblastic lymphoma/leukemia, and rhabdomyosarcomas, in comparison with 33 cases of MCC, to determine the specificity of the paranuclear dot-like CD99 expression in MCC.

RESULTS

Twenty MCC (60%) demonstrated focal expression of CD99 and of those, 14 (42.4%) showed the characteristic paranuclear dot-like expression. CD99 was also paranuclear positive in 4 of 11 (36%) SCC, in 3 of 7 (43%) EWS/PNET, in 1 of 6 (16%) lymphoblastic lymphoma/leukemia cases, in 3 of 3 (100%) rhabdomyosarcomas and all melanomas were negative for the CD99 reaction.

CONCLUSION

CD99 paranuclear dot-like expression was not exclusive of the MCC compared with several neoplasms included in its differential diagnosis. This expression is not a great diagnostic aid.

Solid pseudopapillary neoplasm of the pancreas in children: a 15-year experience and the identification of a unique immunohistochemical marker

PURPOSE

To review our 15-year experience in the management of children with solid pseudopapillary neoplasm (SPPN) of the pancreas at a single pediatric institution, to delineate a unique immunohistochemical marker for SPPN, and to analyze cumulative data on this rare entity in the literature.

METHODS

We did a retrospective analysis of the demographic data, clinical presentation, immunohistochemical characteristics, surgical approach, and long-term outcomes of all patients diagnosed with SPPN between 1997 and 2012.

RESULTS

There were 6 patients in the series, 5 females and 1 male. Median age at presentation and at surgery was 15 years (11-18 years). Abdominal pain was the presenting symptom in 5 cases and jaundice in 1 case. Two patients had a pancreatic head tumor and underwent a pylorus-preserving pancreaticoduodenectomy. Two patients had the tumor in the pancreatic tail and underwent a distal pancreatectomy with splenectomy. Two patients had the tumor in the pancreatic body and underwent a distal pancreatectomy with splenectomy in one case and with preservation of the spleen in the other. All tumors were completely resected with pathologic margins free of disease. The median maximum diameter was 6.8 cm (3 to 15 cm). On immunohistochemistry the tumors exhibited different combinations of non-specific markers like chromogranin, vimentin and neuron-specific enolase, but all tumors showed the highly SPPN-specific paranuclear dot-like immunoreactivity pattern for CD99 in the solid as well as in the pseudopapillary areas. No patient had metastasis at presentation. Median follow-up was 6.5 years (6 months to 15 years). There were no recurrences, no long-term metastasis, and all patients are disease-free.

CONCLUSION

Our series supports the concept that complete resection is necessary to achieve the best possible long-term results. Additionally, we demonstrate that SPPN exhibits a very unique immunostaining pattern for CD99 that is present in all cases.