[473] Dermatomyofibroma: Clinicopathologic and Immunohistochemical Analysis of 56 Cases and Reappraisal of a Rare and Distinct Cutaneous Neoplasm

T Mentzel, H Kutzner. Dermatopathologie Bodensee, Friedrichshafen, Germany

Background: Dermatomyofibroma represents a rare and distinct benign cutaneous mesenchymal neoplasm of fibroblastic/myofibroblastic differentiation. A large series has been analyzed to further characterize the clinicopathologic spectrum of this entity.
Design: We examined 56 cases of dermatomyofibroma from our routine and referral files to evaluate histologic features. Immunohistochemistry was performed and clinical follow-up was obtained.
Results: 40 patients were female and 8 were male (gender was unknown in 8 cases). Patients age ranged from 3 to 51 years (mean: 30.85 years; median: 30 years). 6 patients were younger than 16 years, and in this age group 3 male and 3 female patients were noted. Neoplasms arose on the shoulder (28%), the upper arm (15%), the neck (13%), the thigh (13%), the chest wall (9%), the back (6%), the axillary fold (4%), and the abdominal wall (4%), and one case each on the forearm, the buttock, and the popliteal fossa. 1 patient presented with two lesions arising simultaneously on both shoulders. Histologically, ill-defined, plaque-like, dermal neoplasms of varying cellularity composed of bland spindled tumor cells were seen in all cases. An infiltration of superficial parts of the subcutis was seen in 23 cases, and in 6 cases deeper parts of the subcutis were involved. Tumor cells contained an ill-defined, pale eosinophilic cytoplasm and fusiform nuclei that were either elongated with tapering edges containing an evenly distributed chromatin or vesicular with small nucleoli and indentations. No significant atypia and no increased proliferativ activity was noted. Tumor cells were set in a collagenous stroma, and in most cases an increased number of elastic fibres was seen. Immunohistochemically, 31 out of 48 cases tested stained at least focally positive for actin, and a focal expression of CD34 was seen in 10 out of 45 cases. The remaining antibodies (S-100, desmin, h-caldesmon, EMA, HHV-8, Factor 13a) were negative. Follow-up information was available in 38 cases (range from 3 to 156 months), and despite marginal or incomplete excision in 17 cases none of the cases recurred or showed progression.
Conclusions: Dermatomyofibroma represents an entirely benign fibroblastic/myofibroblastic dermal neoplasm, arises often but not exclusively in the shoulder and upper arm regions of young females, and has to be distinguished from DFSP, smooth muscle tumors, neurofibroma, desmoplastic spindle cell nevus, perineurioma, cutaneous myofibroma, fibrous hamartoma of infancy, and connective tissue nevus.
Category: Dermatopathology

Tuesday, March 10, 2009 1:00 PM

Poster Session IV # 60, Tuesday Afternoon