Papillary thyroid carcinoma (PTC) is by far the most common thyroid malignancy (over 85%) of all the thyroid cancers. It has excellent prognosis and 10-year survival rate in most of the cases (95%). Most of the tumors are indolent and do not recur or metastasize after removal. However, widespread metastases to lung, skeleton, central nervous system and, occasionally, other organs may be observed. In rare instances, this disease may metastasize to the pleura and manifest as a malignant pleural effusion (MPE) and portend poor prognosis. This article reports the cytomorphologic and immunocytochemical findings of a female patient with a symptomatic pleural effusion resulting from PTC metastatic to the pleura. Pleural fluid cytology revealed abundant papillary clusters with relatively nuclear pleomorphism, intranuclear cytoplasmic inclusions and nuclear grooves, small and distinct nucleoli as well as small discrete vacuoles. Psammoma bodies were not seen. Immunocytochemical staining was positive for TGB, EMA, Ber-EP4, CK19, and negative for TTF-1. Metastasis of PTC to pleural fluid is extremely rare and diagnosing the disease by cytology is challenging and requires medical expertise as well as knowledge of clinical context and immunocytochemical staining. Additionally, a cytologic diagnosis of MPE due to PTC provides important treatment information and plays an important role in prognosis.

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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.