Fig. 2.

A. Microscopic description shows an infiltrating malignant appearing neoplastic process. The tumor cells are arranged in infiltrating sheets with a desmoplastic fibrotic background stroma. They demonstrate a high nucleus to cytoplasm (N/C) ratio. The scant cytoplasm is eosinophilic where identifiable. The nuclei are pleomorphic with variable number of vacuolar inclusions, prominent and sometimes multiple nucleoli, with fine chromatin. There is scattered mitosis present. B, C, D. Immunohistochemical staining shows strong diffuse cytoplasmic and membranous reactivity to CD56 (B) and CD99 (C) and a Ki-67 (D) nuclear labeling of approximately 40% in tumor cells.