Indeterminate fibrohistiocytic lesions of the skin - Is there a spectrum between dermatofibroma and dermatofibrosarcoma protuberans?

Routine histology and immunohistochemistry can usually distinguish dermatof ibroma (DF) and dermatofibrosarcoma protuberans (DFSP). DF generally expres ses factor XIIIa whereas DFSP generally expresses CD34. The authors report 10 cutaneous fibrohistiocytic lesions combining clinical, histologic, and i mmunohistochemical features of both DF and DFSP. The lesions had an average size of 1.2 cm (range, 0.4-2.7 cm), and occurred on the trunk (n = 6), ext remities (n = 3), and face (n = 1) of four men and six women (average age, 30.6 yrs; age range, 15-50 yrs). Eight lesions exhibited acanthosis and den sely cellular fascicles with focal storiform areas. All had keloidal collag en, infiltrated the subcutis in a honeycomb pattern, and had low mitotic co unts (0 to 4 mitoses per square millimeter). All were diffusely immunoreact ive for factor XIIIa (30%-60% of the neoplastic cells) as well as CD34 (20% -70%). This series raises the possibility of a biologic spectrum between DF and DFSP; however, double-immunolabeling studies showed no notable coexpre ssion of factor XIIIa and CD34 by individual cells, suggesting coexistence of two different cellular populations. After an average follow up of 22.3 m onths (range, 10-46 mos) in six cases, a single recurrence was documented. The ambiguous histologic features and the potential for local recurrence su ggest that performing a complete excision may be prudent in these diagnosti cally indeterminate lesions.