A 36 year-old female presents with this painless nodule on her lower leg. She notes that its size fluctuates, but that it is usually around 1 cm in diameter. When squeezed, the nodule dimples inward.

Unknown 13a


Unknown 13b

A biopsy is performed, and a representative section is shown here.

What is this lesion?

A. Dermatofibroma
B. Nodular basal cell carcinoma
C. Melanoma
D. Spitz nevus
E. Hemangioma




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The diagnosis in this case is dermatofibroma. Dermatofibromas are benign tumors usually seen on the legs of young to middle-aged women. They usually present as tan, firm papules. Curiously, they tend to dimple inward if you squeeze them at the margins.

Under the microscope, the tumor is composed of bland, spindle-shaped cells which occasionally extend into the subcutaneous fat. You can see them making streaming patterns and sort of growing every which way in the image above.

Nobody really knows what causes these tumors. The good news is that their behavior is indolent – so usually surgical excision is curative.

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