Amelanotic Malignant Melanoma with Dense Pleural Thickening Mimicking Malignant Mesothelioma

Abstract

A 51-year-old man was diagnosed with stage IIC nodular malignant melanoma (T4bN0M0) of the right upper arm. The tumor was treatment-refractory, and left-sided pleural effusion emerged 1.5 years later. Aspiration of pleural fluid revealed abundant amelanotic, atypical cells that resembled epithelial malignant mesothelioma or lung adenocarcinoma cells; these cells were positive for melanoma-associated antigen recognized by T cells (MART-1)/Melan-A, HMB-45, and S-100 on immunocytochemistry. Thoracic computed tomography (CT) revealed marked diffuse pleural thickening in the left hemithorax that mimicked malignant mesothelioma; thus, the present report describes the unique cytological and radiological findings of this case.

Pleural effusion as the initial manifestation of metastatic melanoma: a case report and literature review

“…For our patient, the left pleura was signi cantly thickened and calci ed so that the puncture needle had signi cant resistance to entry. Pleural thickening can indicate several diseases, such as malignant mesothelioma, tuberculous pleuritis, primary or secondary pleural lymphoma, metastatic lung cancer, ectopic thymoma, and sarcomatoid carcinoma (21) . The differential diagnosis included mesothelioma, adenocarcinoma, primary pleural sarcoma, thymic epithelial tumors, lymphoma, and other metastatic tumors (7) .…”

“…Other common causes of BPEs include parapneumonic and posttraumatic (23) . Melanin pigment is an indicator of malignant melanoma which can distinguish this disease from other morphologically similar tumors, such as lung adenocarcinoma and malignant mesothelioma (21) . However, malignant melanoma does not always present with melanin in pleural uids which increases the di culty of diagnosis.…”

“…However, malignant melanoma does not always present with melanin in pleural uids which increases the di culty of diagnosis. A combination of immunohistochemistry and immunocytochemical staining techniques are powerful tools for de nitive diagnosis in cases of amelanotic or hypomelanotic melanoma (21) .…”