A 57-year-old man presented with a 2-year history of a slowly enlarging, asymptomatic nodule on the right forearm. There was no history of trauma to the area, and the patient's medical history was otherwise insignificant.Physical examination disclosed a 2.0 X 2.5-cm, erythematous, hard, freely mobile, elevated nodule on the anterior aspect of the proximal right forearm (Fig 1). No lymphadenopathy was present. The remainder of the physical examination was normal.Representative sections of an excisional biopsy specimen are shown (Figs 2 and 3).What is your diagnosis? Figure 1.Figure 2.Figure 3.Clinicians, local and regional societies, and residents and fellows in dermatology are invited to submit quiz cases to this section. Cases should follow the established pattern and be submitted double-spaced and in triplicate. Photomicrographs and illustrations must be clear and submitted as positive color transparencies (35 mm). Do not submit color prints unless accompanied by original transparencies. If photomicrographs are not available, the actual slide from the specimen will be acceptable.
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