Ossifying fibromyxoid tumor of the retroperitoneum

A case of ossifying fibromyxoid tumor (OFMT) in an unusual site, the retroperitoneum, in a 71 year old Japanese man Is reported. The well demarcated tumor contained a large amount of mature bony tissue within the tumor. The tumor cells were round to spindle‐shaped, and showed a high cellularity in some areas and were loosely arranged in other areas. Although the majority of tumor cells expressed vimentin, neuron specific enolase and Leu‐7, there were no tumor cells positive for S‐100 protein, myogenic or epithelial markers. We would like to emphasize that tumors classified as OFMT contain a wide spectrum of histologic features and heterogeneity.