Ossifying fibromyxoid tumor: invariable ultrastructural features and diverse immunophenotypic expression.

Ossifying fibromyxoid tumor (OFMT) is a rare enigmatic soft tissue tumor, the origin of which is still uncertain. The authors report on 3 cases of OFMT arising in the trunk and head and neck regions of adults. Two recurred and one was suspected to have metastasis. All tumors consisted of multiple nodules, in which round or polygonal tumor cells were arranged in sheets or cords within a fibromyxoid background. Characteristic shell-like bone tissues were recognized in all tumors. Based on the grading system proposed by Folpe et al., 2 cases were designated as malignant OFMT and 1 as typical. In addition to S-100 protein, cytokeratin and neuronal markers (neurofilament, CD56 or CD57) were detected in 1 and 2 tumors, respectively. The salient and invariable ultrastructural features included reduplicated basal laminas, which seem to be crucial for the diagnosis.