Cytological diagnosis of metastatic melanoma presenting as an isolated pleural effusion: A case report

Malignant melanoma (MM) is a malignant melanocytic neoplasm that occurs mainly in the skin but it can also involve any tissue. It has the capacity to metastasize widely and quickly to various sites without any intermediate stops, sometimes many years after treatment of the primary tumor. It is almost impossible to predict which organ system will be invaded by melanoma from a given primary site. We report the cytomorphologic and immunocytochemical findings of a male patient with isolated pleural metastasis of MM without pulmonary parenchymal metastatic involvement after 10 years of progression-free survival. Pleural fluid cytology revealed epithelioid cells of variable sizes and configuration isolated or in clusters with abnormal hyperchromatic nuclei, irregularly-shaped nucleoli, abundant eosinophilic cytoplasm, multinucleated giant cells, intranuclear cytoplamic inclusions as well as many cytoplasmic melanin pigmented tumor cells. Immunocytochemical markers for melanoma HMB-45 and S-100 were positive. Metastasis of MM to pleural fluid is rare and diagnosing the disease by cytology is challenging and requires medical expertise as well as knowledge of clinical context and immunocytochemical staining evaluation.