Australian Society of CytologyCase of the Month
March 2004 - Answer and Discussion
Metastatic malignant melanoma.
Answer:
The smears show clusters of atypical, polygonal, epithelioid cells containing enlarged, vesicular nuclei surrounded by a fair amount of finely granular cytoplasm.
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A variable amount of nuclear pleomorphism and atypia is noted.
Single and multiple eosinophilic nucleoli are present, with some macronucleoli also seen.
A small number of foamy macrophages are present and many cells contain light brown melanin pigment.
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Discussion:
Melanoma in effusions
Effusions due to metastatic malignant melanoma tend to be bloody and inflammatory.
The melanoma cells are loosely cohesive, round to oval in shape and vary in size.
The cytoplasm is abundant and often finely vacuolated, although gross vacuolation can occur.
Melanin pigment is present in a minority of cases and will often be associated with the background histiocytes.
Malignant nuclei are large, round, eccentrically placed and can exhibit multinucleation.They are hyperchromatic with single to multiple prominent macronucleoli.
Due to the abundant cytoplasm, cells do not have a high N:C ratio.
Care must be taken in diagnosis as melanoma is an excellent mimic and can strongly resemble reactive mesothelial and adenocarcinoma cells.
Vacuolation, multinucleation, prominent nucleoli and cell-in-cell engulfment are common features to all three. Gross vacuolation can push the nucleus of the melanoma cell to the periphery of the cytoplasm mimicking a signet ring adenocarcinoma for example.
Immunocytochemical markers such as S100, HMB45, MART-1 and MELAN A can be helpful in the diagnosis of amelanotic cases where no melanin pigment is seen. Although, results must be interpreted with caution as mesothelial and adenocarcinoma cells may express S100 protein and HMB45 may be expressed in cases of breast carcinoma. This case did not require immunocytochemistry as the melanin pigment was obvious and the patient’s past history indicated a diagnosis of melanoma.
Reference:
- Geisinger K,Raab S,Stanley M,Silverman J,Abati A, Modern Cytopathology, Churchill Livingstone 2004.
