Concurrent Merkel cell carcinoma and Bowen's disease of the thigh

    An 88-year-old Caucasian female presented a left thigh skin lesion (Figure 1), which was clinically suspected to be a pyogenic granuloma. After a diagnosis of Merkel cell carcinoma was made from the biopsy, the entire lesion was completely excised with clear margins. Microscopically (Figures 2 and 3), the dermal lesion was a highly cellular and mitotically active malignant tumor composed of undifferentiated small round blue cells. The tumor exhibited a somewhat trabecular pattern with extensive necrosis. The neoplastic cells were medium in size with scant rims of cytoplasm and hyperchromatic nuclei with a salt and pepper chromatin pattern without discernable nucleoli. Some of nuclei showed nuclear molding with smudgy chromatin. Numerous apoptotic bodies were also noted. Immunostains demonstrated that the tumor cells were positive for cytokeratin 20 with a characteristic paranuclear dot-like pattern (Figure 4). The tumor cells were focally positive for synaptophysin and chromogranin but were negative for cytokeratin 7 and cytokeratin 5/6. Ultrastructurally, the tumor cells showed relatively scant cytoplasm with scattered membrane-bound electron dense core granules in the subplasmalemmal location. The clinical finding, histopathologic features, ultrastructural observation, and immunoprofile were consistent with primary cutaneous MCC rather than a metastatic small cell carcinoma from the lung.

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