Deep Penetrating Dermatofibroma As A Variant of Benign Cellular Fibrous Histiocytoma

Deep penetrating dermatofibroma is a histologically distinctive variant of dermatofibroma that generally occurs on the lower extremities of adults. The tumor penetrates into the subcutis extending along the septae. The clinicopathological distinction between deep penetrating dermatofibroma extending into the subcutis and dermatofibrosarcoma protuberans (DFSP) may be challenging. Immunohistochemically, the tumor cells of dermatofibroma stain for Factor XIIIa and are negative for CD34. DFSP shows the opposite staining profile.

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Slide 1: 58 year-old woman with a thigh lesion. Low power examination reveals a lesion that is primarily situated within the deep dermis.

Slide 2: There is a proliferation of spindled cells with concomitant dermal sclerosis.

Slide 3: The cells exhibit some element of cytologic heterogeneity in terms of nuclear size and shape. It is of moderate cellularity without significant atypia nor is there mitotic activity. title=

Slide 4: The Factor XIIIa preparation highlights the spindled infiltrate typical for a dermatofibroma/benign fibrous histiocytoma.

Slide 5: Factor XIIIa high magnification. Overall the findings are compatible with a deep seated variant of dermatofibroma. This particular unusual morphologic variant of dermatofibroma is considered a form of benign cellular dermatofibroma. These lesions can recur.