Fig. 2

Microscopic features of the renal follicular dendritic cell sarcoma. a The neoplastic cells formed syncytial sheets with indistinct cell borders. One of the most characteristic findings was the striking lymphocytic infiltration throughout the tumor. The nuclei of the tumor cells showed grooves and lobulation, vesicular chromatin, and prominent nucleoli. The pleiomorphism was focally marked (magnification factor of 200x). b Despite the pleiomorphism, the mitotic rate was relatively low (magnification factor of 400x). c The neoplastic cells showed diffuse, strong positivity with CD21 (magnification factor of 200x). d The tumor cells displayed diffuse and moderately strong membranous staining with somatostatin receptor 2 A (magnification factor of 200x). e The neoplastic cells expressed MDM2 strongly and diffusely. This finding could lead to an erroneous diagnosis of dedifferentiated liposarcoma, especially in a case of a retroperitoneal tumor (magnification factor of 200x). f The MDM2 FISH analysis demonstrated more than five MDM2 (red) signals in the tumor cells, indicating gene amplification (magnification factor of 1200x)