Metastatic malignant melanoma in liver aspirate: cytomorphologic distinction from hepatocellular carcinoma

Hepatic metastases of malignant melanoma are not unusual and frequently occur with a clinically long latent period following resection of a cutaneous or ocular primary. Due to its overlapping cytomorphology with a primary hepatocellular carcinoma, diagnostic difficulties may arise on fine-needle aspiration of these lesions if the clinical history of melanoma is not known. Thirty-two cases of metastatic melanoma in the liver and primary hepatocellular carcinoma were studied. Aspiration was performed under ultrasound guidance using 22-gauge spinal needle. Slides were stained with Diff-Quik and Papanicolaou stain; cell blocks were stained with H&E. A panel of immunostains was performed using conventional methodology. Of the 12 cytologic parameters assessed, the most helpful in making a metastatic melanoma diagnosis were the presence of sheet-like architecture, plasmacytoid and/or biphasic (epithelioid/spindled cell) morphology, cytoplasmic tails, necrosis, and cytoplasmic melanin-like pigment. For hepatocellular carcinoma, the presence of trabeculae, perivascular cellular clustering, endothelial wrapping, and centrally located nuclei with granular cytoplasm were helpful features. In selected cases, IPOX studies were critical in arriving at the correct diagnosis.