CD99 in malignant hematopoiesis

The CD99 gene encodes a transmembrane protein that is involved in cell differentiation, adhesion, migration, and protein trafficking. CD99 is differentially expressed on the surface of hematopoietic cells both in the myeloid and lymphoid lineages. CD99 has two isoforms, the long and short isoforms that play different roles depending on the cellular context. There has been extensive evidence supporting the role of CD99 in myeloid and lymphoblastic leukemias. Here we review research findings related to the CD99 in malignant hematopoiesis. We also summarize the significance of CD99 as a therapeutic target in hematological malignancies.

Ewing sarcoma with myxoid stroma: Case report of an unusual histological variant

We describe the case of a Ewing sarcoma with prominent myxoid stroma of the temporal bone in a 26-year-old female. Histologically, the tumor exhibited a fascicular growth pattern of round to spindled cells with a minimal amount of pale eosinophilic to clear cytoplasm and oval or spindled nuclei with finely dispersed chromatin and small nucleoli. Myxoid changes were prominent (>50%), with reticular or pseudoacinar growth of the loosely cohesive cells. The tumor showed strong expression of CD99, FLI1, and CD56 and was positive for the EWSR1-FLI1 fusion transcript. The diagnosis of Ewing sarcoma with myxoid stroma (myxoid variant) is particularly problematic owing to the large number of potential mimics. The tumor extends the morphologic spectrum of Ewing sarcoma beyond the previously described histological variants, and broadens the differential diagnosis. For any round/spindle cell sarcoma, prominent myxoid stroma and CD99 immunoreactivity should prompt consideration for molecular studies that include analysis of both EWSR1 and FLI1.

[Significance of P504s in distinction between solid pseudopapillary tumor of pancreas and pancreatic neuroendocrine tumors]

OBJECTIVE

To study the significance of P504s in differential diagnosis between solid pseudopapillary tumor of the pancreas (SPTP) and pancreatic neuroendocrine tumors (PanNET).

METHODS

Forty-three patients with SPTP and 41 patients with PanNET encountered during the period from 2007 to 2014 were recruited. Immunohistochemical study for vimentin, CD10, chromogranin A, synaptophysin, beta-catenin, CD99 and P504s in SPTP and PanNET was performed. The diagnostic value of P504s in differentiating SPTP from PanNET was analyzed.

RESULTS

Immunohistochemical study showed that vimentin, CD10, chromogranin A, synaptophysin and CD99 were expressed both in SPTP and PanNET. All cases of SPTP showed granular cytoplasmic expression of P504s, whereas those of PanNET were negative.

CONCLUSION

P504s is a sensitive and useful marker for SPTP and can be used in the distinction between SPTP and PanNET.