A 73-year-old man had a 2-month history of a rapidly growing painless mass on the left upper arm.
Fig. 1. An erythematous mass on the left upper arm.
Skin examination revealed an erythematous mass measuring 2.5×2.5 cm on the left upper arm (Fig. 1). There was no regional lymphadenopathy. General physical examination and laboratory tests revealed normal findings. Punch biopsy was taken and histopathological examination revealed the tumor was located in the deep dermis, partly extending into subcutaneous tissue. The tumor cells were arranged in dense cohesive sheets with a variable trabecular pattern. The individual cells had a monomorphous nature with round to oval, vesicular nuclei and scanty cytoplasm (Fig. 2). Mitotic figures were not seen. Immunohistochemically, positive results for neuron-specific enolase (NSE), chromo- granin, synaptophisin and cytokeratin 20 were obtained. Leucocyte common antigen and S-100 were negative. Especially, staining for cytokeratin 20 showed perinuclear dot-like patterns (Fig. 3). Chest and abdomino-pelvic CT scan did not show abnormal findings. Whole body PET also showed normal findings. According to these findings, the diagnosis of Merkel cell carcinoma was made. The tumor was excised up to the muscle fascia with a 3 cm margin, and repair with full thickness skin graft was performed. And axillary lymph node dissection (7 lymph nodes) based on the intraoperative lymphangio- graphic finding was performed. But tumor cells were not found in axillary lymph node sections.
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Fig. 2. The tumor cells with anastomosing and interdissecting trabecular arrangement in the dermis (A: H&E. x40). The tumor cells show round to oval vesicular nuclei and scanty cytoplasm and inconspicuous nucleoli, evenly dispersed chromatin (B: H&E, x400).
The patient underwent post-operative radiotherapy on the lesion and left axillary node area for 4 weeks (25 times, total 5,000 cGy). After 2.5 years, the patient is still in state of complete remission with no sign of disease recurrence in both the whole body PET and CT scan.
Fig. 3. Tumor cells showed perinuclear dot-like staining with CK20 (x400).