Effusion cytomorphology and immunocytochemistry of malignant melanoma: five cases of melanotic melanoma and one case of amelanotic melanoma.

Effusion cytological analyses of amelanotic malignant melanoma (AMM) are very rare and no concise description of AMM related cytomorphologic features using effusion have been reported. Here, we report the cytomorphological, immunohistochemical, and immunocytochemical findings in the effusion cytology of six cases of malignant melanoma (MM), one case of AMM, and five cases of melanotic malignant melanoma. Papanicolaou-stained smears exhibited conspicuous nucleoli, multinucleation, and cytoplasmic vacuolization in all of the MM cases. In addition, the AMM case displayed numerous mitotic figures and intranuclear cytoplasmic inclusions. With regard to the immunohistochemistry findings, all six cases of melanoma were positive for Melan-A/MART-1, HBME-1, and S-100. In the immunohistochemistry analyses, five of six cases of melanoma were positive for WT-1, as was the AMM specimen. Furthermore, because the effusion analysis of malignant mesothelioma proved positive for WT-1, it should be noted that WT-1 effusion analysis is not an appropriate means to distinguish between MM and malignant mesothelioma. We suggest that it is important to recognize cytomorphologic characteristics, such as melanin pigment, conspicuous nucleoli, multinucleation, and cytoplasmic vacuolization, and to choose appropriate antibodies for the correct diagnosis of MM in effusion.