Aspiration cytodiagnosis of metastatic Merkel-cell carcinoma

A case of metastatic Merkel-cell carcinoma to lymph nodes on the left side of the neck and left parotid is described. The primary was at the left side of the cheek and bridge of the nose. The cytologic features in needle aspirates of metastases included increased cellularity, discohesive or loose groups of small-to-medium size malignant cells with uniform, round-to-oval nuclei, delicate nuclear membranes, fine chromatin, multiple micronucleoli, and scanty cytoplasm. Additionally, rare intermediate filament "buttons" and frequent mitotic figures were found. The primary tumour showed similar features. On immunostaining, although a positivity for chromogranin was noted in the primary tumour, it was found to be negative in the cytologic material. All other histochemical and immunostains were found to be negative in both the primary and metastatic neoplasm. The problems in differential diagnosis from other small cell tumours and the features of this unique tumour that may be helpful in the diagnosis are discussed.