Question 1:
A 58-year-old male with a history of multiple pathologic skeletal fractures presented with an asymptomatic approximately 1.5 cm nodule on the plantar aspect of his left foot. He had a remote history of injury to the area. An excisional biopsy was performed (Figures 1-5).
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Figure 1

Figure 2

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Figure 5

Which of the following is the best diagnosis?