DIFFERENTIAL EXPRESSION OF FACTOR-XIIIA AND CD34 IN CUTANEOUS MESENCHYMAL TUMORS

The histogenetic relationship amongst various dendritic cells of the dermis which may express markers including factor XIIIa (FXIIIa) or CD34 remains unclear. In this study we utilized a sensitive indirect immunoperoxidase staining technique to identify CD34 and FXIIIa, as well the monocyte/macrophage markers KP-1 and MAC 387 expression in a variety of cutaneous dermal tumors of mesenchymal origin to see if differential expression of CD34 vs FXIIIa exists. Tumors studied included dermatofibroma (DF) (N = 10), keloid (N = 9), atypical fibroxanthoma (AFX) (N = 3), and dermatofibrosarcoma protuberans (DFSP) (N = 7). DF were all composed of FXIIIa+ spindle-shaped and stellate tumor cells (mean score = 4.9 or greater-than-or-equal-to 75% FXIIIa+) as previously reported, but these cells rarely (< 10%) expressed CD34. Six of 7 DFSP were found to be > 75% CD34+ and FXIIIa negative, while one DFSP was negative for both CD34 and FXIIIa. In all DFSP, there were trapped FXIIIa+ cells which were distinct from the spindle-shaped tumor cells. AFX showed sparse populations of FXIIIa+ cells in the stroma (mean score = 1.33 or 10-25% positive), which were distinct from the atypical giant cells characteristic of these tumors. Keloid similarly contained trapped FXIIIa+ cells (mean score = 0.44 or < 5% positive) that were distinct from the spindle-shaped fibroblasts of the tumor mass. Dendritic and spindle-shaped cells within these tumors were consistently both KP-1 and Mac-387 negative, while all lesions studied were characterized by scattered round, histiocytic cells which were KP-1+ and/or Mac-387+ irrespective of tumor cell type. We suggest that these tumors can be delineated by their relative degrees of FXIIIa and CD34 expression and that these neoplasms may be a useful link with which to study the relationship between CD34+ cells and dermal dendrocytes.