An unusual soft tissue tumor with features of angiomatoid malignant fibrous histiocytoma composed of bimodal CD34 and factor XIIIa positive dendritic cell subsets. CD34 and factor XIIIa in angiomatoid MFH.

CD34 and factor XIIIa (FXIIIa) antibodies delineate subsets of embryonic dendritic stromal stem cells that persist in adult mesenchyme. CD34 stains interstitial and adventitial dendritic cells that may function as multipotential precursor cells. FXIIIa+ dendrophages are tissue histiocytes active in tissue repair. Angiomatoid malignant fibrous histiocytoma (AMFH) is an enigmatic fibrohistiocytic tumor with limited vascular features. We examined an unusual soft tissue tumor from the nasolabial subcutis of a 57 year old man that showed histologic features of AMFH. Most of the tumor cells expressed CD34. 10-30% of the tumor cells were FXIIIa+ dendrophages. Sinusoidal areas were largely composed of FXIIIa+ cells that also expressed HLA-DR and CD68 suggesting macrophage differentiation. CD31 and Factor VIII antigen highlighted capillaries and single cells among the CD34+ tumor cells. The vessels had actin+ myopericytes and there were single actin+ tumor cells. Electron microscopy showed primitive dendritic cells and fewer histiocyte-like cells. The Ki 67 index was 15% including both FXIIIa+ and CD34+ cells. The patient is disease free three years after wide excision. We conclude that this AMFH-like neoplasm is a fibrohistiocytic tumor in which CD34+ fibroblast-like precursors and FXIIIa+ tissue dendrophages combine to build both sinusoidal tissue with endothelial and macrophage elements as well as capillary vascular tissue that is invested with myopericytes. Study of additional AMFH lesions from this standpoint is desirable.