DEEP PENETRATING DERMATOFIBROMA VERSUS DERMATOFIBROSARCOMA PROTUBERANS - A CLINICOPATHOLOGICAL COMPARISON

A study of the clinical, histological, and immunohistochemical feature s of 20 cases of deep penetrating dermatofibroma (DPDF) and eight case s with 14 specimens (eight primary, one reexcision, five secondary tum ors) of dermatofibrosarcoma protuberans (DFSP) showed distinct entitie s. Clinically, DPDF usually appeared as a nodule (similar to 2 cm) of the (lower) limbs, whereas DFSP affected the trunk (shoulder) with irr egularly arranged plaques or nodules (>5 cm). Histologically, DPDF sho wed a regular silhouette with a smooth, nodular (four of 20) or scallo ped (16 of 20) lower margin and variable sclerosis (nine of 20); DFSP, irregularly infiltrated fatty tissue in a lacelike/honeycomb (eight o f 14), multilayered (three of 14), or mixed pattern (three of 14), but without sclerosis. Immunohistochemically, DPDF was mostly negative wi th QBEnd 10 (CD34; 18 of 20) but positive for factor XIIIa (17 of 20), actin (HHF35; 10 of 20), and metallothionein (MT; 12 of 20). DFSP was positive for CD34 (13 of 14), yet with some sparing of central tumor parts, highly cellular tumor nodules, and myxoid areas; factor XIIIa a nd MT were consistently negative, as was HHF35 in 11 of 14 cases. In a multivariate analysis of histologic and immunohistochemical criteria, the combination of sclerosis and labeling with MT was most valid (p = 0.0001) for diagnosis: all DPDF showed either labeling with MT in ''e arly'' (metabolically active) lesions or sclerosis in ''late'' lesions , not present in DFSP.