A rare case of an exotic pleural mesothelioma – the lymphohistiocytoid variant

Objectives: Malignant pleural mesothelioma is a rare tumor entity among thoracic malignancies. In addition to the three main histologic subtypes (epithelioid, sarcomatoid, biphasic), there are also rare histologic variants that present challenges even to experienced pathologists. These major subtypes have implications for the prognosis and management of patients diagnosed with this aggressive tumor.

Methods: A 71-year-old male patient presented in good general condition for further diagnosis of right pleural thickening without pleural effusion. In the absence of clinical symptoms and in good cardiopulmonary condition, the finding had come to attention during an externally performed diagnostic procedure using CT of the thorax to exclude pulmonary artery embolism after thrombophlebitis of the great saphenous vein on the right side. There was no known exposure to asbestos. Diagnostic video-assisted thoracoscopy revealed spherical, reddish-livid deposits on the parietal pleura and diaphragm. The visceral pleura showed no abnormalities. Representative biopsies were sent for histopathologic examination.

Results: Complex histologic workup revealed the presence of pleural mesothelioma of lymphohistiocytoid subtype. Differentially, Hodgkin's lymphoma, thymic neoplasia and lymphoepithelial tumors must be considered. Characteristic were strong CK18, AE1/3, WT1, D2-40, GATA3, EMA and calretinin expressions and a conspicuous presence of the lymphoid component of the cytotoxic T cells. BAP1 showed preserved nuclear expression. CD68 and CK5/6 were found to be negative. There was no evidence of Epstein-Barr virus-related infection. Furthermore, PD-L1 expression was 80%, so immunotherapy was initiated.

Conclusion: The lymphohistiocytoid variant of malignant mesothelioma is rare with only very few cases described in the literature so far. It is characterized by mesothelial cells with a histiocytelike appearance and an associated dense lymphoid infiltrate. Nevertheless, detailed immunohistochemical workup is necessary to allow accurate differentiation of subtypes for final diagnosis and thus further clinical treatment and therapeutic options.

Publication History

Article published online:
01 March 2024