Abstract
Background : Japanese practioners rarely encounter malignant effusion due to malignant melanoma in routine cytopathology because the prevalence of melanoma is lower in Japan than in western countries. We retrospectively reviewed effusion samples diagnosed as malignant melanoma.
Cases : Six patients (2.3%) with malignant effusions diagnosed as malignant melanoma were retrieved from hospital files out of 406 tissue samples from 256 patients diagnosed with malignant melanoma between 1989 and 2008. Patients were five men and one woman ranging from 26 to 72 years old (median 56). All had cutaneous melanoma. Effusion appeared 5.5 to 135 (mean 31.7) months after primary lesion resection. The prognosis was dismal, and patients died 18 to 45 (mean 38.2) days after the appearance of malignant effusion. Prominent cytological features included lack of cellular cohesion (6/6), prominent nucleoli (6/6), multinucleation (5/6), melanin pigment (4/6) and cytoplasmic vacuolization (5/6).
Conclusions : The diagnosis of malignant melanoma in effusion can be challenging when tumor cells lack melanin pigment especially in the absence of a clinical history. Differential diagnosis included malignant mesothelioma, reactive mesothelial cells, and poorly differentiated adenocarcinoma. A combination of morphology and immunocytochemical analysis using MART1/melan A, HMB45, and S100 antibodies and the acquisition of a clinical history should yield an accurate diagnosis.
