The distinction between
dermatofibroma, particularly cellular variant, and
dermatofibrosarcoma protuberans in excisional biopsies is usually straightforward. However, a separation between the two may be sometimes challenging, especially in superficial biopsies. Although
factor XIIIa and CD34 immunostains are useful in differentiating
dermatofibroma and
dermatofibrosarcoma protuberans in most instances, focal CD34 positivity may be seen in cellular
fibrous histiocytoma. Some cases reveal overlapping immunostain results. D2-40 identifies a 40-kDa O-linked
sialoglycoprotein present on a variety of tissues including testicular
germ cell tumors as well as lymphatic endothelium. In this study, we investigated the utility of D2-40 in separating
dermatofibroma from
dermatofibrosarcoma protuberans and compared the results with other commonly used immunostains. Fifty-six cases of
dermatofibroma (including six cellular variant) and 29 cases of
dermatofibrosarcoma protuberans were retrieved from the archives of Department of Anatomic Pathology at Sunnybrook Health Sciences Center in University of Toronto. We applied
factor XIIIa, CD34, and monoclonal mouse anti-D2-40 immunostains to
formalin-fixed,
paraffin-embedded tissue sections. All 56 (100%) cases of
dermatofibroma demonstrated strong and diffuse immunoreactivity to D2-40 in the spindle cells and stroma. Similarly,
factor XIIIa showed strong and diffuse positivity in the spindle cells. Nearly all
dermatofibromas were negative for CD34 except one case revealing focal positivity. None of
dermatofibrosarcoma protuberans cases were labeled by D2-40, although four cases showed weak and patchy background staining in contrary to diffuse, strong, and crisp staining seen in
dermatofibromas. Our results indicate that D2-40 seems to be a sensitive immunohistochemical marker for
dermatofibromas, including cellular variant. Focal and faint D2-40 staining may be seen in the stroma of
dermatofibrosarcoma protuberans. Our findings suggest that D2-40 can be used as a complementary immunostain to
factor XIIIa and CD34 in problematic and challenging cases on superficial biopsies.