Amelanotic Malignant Melanoma with Dense Pleural Thickening Mimicking Malignant Mesothelioma

Our plain-English summary of Amelanotic Malignant Melanoma with Dense Pleural Thickening Mimicking Malignant Mesothelioma, by T. Saraya, M. Fujiwara, K. Morita, et al (Internal Medicine, 2019).

The study

• Authors: T. Saraya, M. Fujiwara, K. Morita, T. Watanabe, Y. Ogawa, H. Takizawa, R.W. Light
• Journal: Internal Medicine
• Published: 2019;58(7):969-972
• Type of article: Case report
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

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.

In plain English

This case report described one 51-year-old man, treated at a university hospital in Japan, whose skin cancer spread to the left pleura, the lining of the chest cavity, and looked like malignant mesothelioma. The cancer was a nodular malignant melanoma of the right upper arm. The article noted that he had no extensive dust exposure and did not mention asbestos. The melanoma did not respond to treatment. Fluid built up around the left lung one and a half years after he was first referred to the authors' hospital. Under the microscope, cells in the fluid resembled epithelioid malignant mesothelioma or lung adenocarcinoma cells, and the tumor showed no melanin pigment. Stains were positive for melanoma markers (MART-1/Melan-A, HMB-45, S100) and negative for markers including calretinin and D2-40, so melanoma was diagnosed. Within two months the pleural thickening grew to 15 mm and covered the whole left side of the chest. He died of respiratory failure two years after his first referral. The authors concluded that careful cytology looking for melanin, together with immunocytochemical staining, can distinguish melanoma from similar-looking cancers.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: case report
• Who was studied: One 51-year-old man with nodular malignant melanoma of the right upper arm, referred to Kyorin University School of Medicine, Japan. No dates are given.
• Exposure: No asbestos exposure was studied, and the article does not mention asbestos. The patient was reported to have had no extensive dust exposure. He was an ex-smoker with 15 pack-years.
• Main results:
  • The patient developed left-sided pleural effusion one and a half years after his first referral.
  • After drainage, CT showed an enhanced and partially thickened left parietal pleura, which suggested pleural metastasis.
  • Cells in the pleural fluid were large, multinucleated and atypical, and resembled malignant mesothelioma (epithelioid type) or lung adenocarcinoma cells.
  • The melanoma showed no evidence of melanin granules (amelanotic).
  • The atypical cells were positive for MART-1/Melan-A, HMB-45, S100 protein and vimentin. They were negative for cytokeratin AE1/AE3, calretinin and D2-40. The patient was diagnosed with malignant melanoma.
  • Pleural fluid markers (CEA, CYFRA 21-1, hyaluronic acid, ADA) were normal. The authors took this to indicate that malignant mesothelioma, lung cancer or tuberculous pleuritis was unlikely.
  • Within two months the pleural thickening expanded to 15 mm and eventually covered the entire left hemithorax.
  • The tumor did not respond to treatment, and the patient died of respiratory failure two years after his initial referral.
• The authors' conclusion: The authors concluded that dense pleural thickening like that of malignant mesothelioma is a possible imaging finding in malignant melanoma. They added that careful cytological examination for melanin pigment, together with immunocytochemical staining, can differentiate malignant melanoma from other malignancies with similar features.
• Limitations the authors state:
  • The authors did not measure the patient's serum soluble mesothelin-related peptides, which they describe as a reliable diagnostic marker for malignant mesothelioma.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Pleural Thickening, Mesothelioma, Pleural Effusion, Lung Adenocarcinoma, S-100, Diffuse Pleural Thickening, Hemithorax.

Related studies

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• Retrosternal and pleural "bridging" fibrosis mimicking malignancy in a patient exposed to asbestos — M.P. Debray, S. Marchand-Adam, et al. (2010)
• Diffuse pleural thickening following heart failure-related pleural effusions in an asbestos exposed patient — M. Evison, P. Barber (2015)
• Rapidly progressing metastatic malignant melanoma mimicking primary pleural tumor: A case report — C. So, T. Yoshida, et al. (2022)
• Pulmonary sclerosing hemangioma presenting with dense spindle stroma cells: a potential diagnostic pitfall — X.Y. Lin, Y. Wang, et al. (2012)
• Increased body mass index is related to apparent circumscribed pleural thickening on plain chest radiographs — Y.C. Lee, C.K. Runnion, et al. (2001)

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