C80-15 Pseudomesothelioma From Adenocarcinoma: A Diagnostic Pitfall in the Setting of Prior Hematologic Malignancy

Lung malignancies typically present with characteristic histopathologic patterns; however, some tumors can be mimics of others which creates significant diagnostic challenges. One such example is pseudomesotheliomatous carcinoma, a rare variant that is histologically carcinoma but originates in the pleura and clinically and radiologically resembles malignant mesothelioma. Pseudomesotheliomatous carcinoma can even mimic mesothelioma under the microscope in the appearance of the cells, thus histologic staining is necessary to distinguish the cancer origins. While most cases arise from a primary lung malignancy, instances originating from other sites, such as the esophagus, have been reported. We present a case of a pleural-based lung lesion initially suggestive of mesothelioma but ultimately diagnosed as adenocarcinoma on histologic evaluation. The patient is a 50-year-old female with a history of T cell prolymphocytic leukemia treated with CHOEP regimen three years prior as well as remote smoking history and asbestos exposure.She presented to the emergency department after three weeks of progressive dyspnea and an abnormal chest Xray. CT angiography of the chest showed nodular thickening along the left basilar pleura with a four-centimeter pleural mass of the left lung apex. CT-guided biopsy of the pleural mass was sent to pathology; the tissue was mostly necrotic and preliminarily read as malignant mesothelioma. Repeat biopsy was sent to an outside institution for review, this stained strongly positive for CK 8/18 and CK7, focally positive for calretinin, and negative for CK 5/6. Although grossly resembling malignant mesothelioma, the final diagnosis was poorly differentiated non-small cell carcinoma favoring adenocarcinoma. Asbestos exposure is a well-established cause of malignant mesothelioma, while T-cell prolymphocytic leukemia and CHOEP therapy have both been associated with an increased risk of secondary solid tumors. This unique case involving a patient with several established risk factors raises important questions about their potential contribution to the development of pseudomesotheliomatous carcinoma. It also depicts the importance of recognizing the possibility of mimicry as prolonged diagnosis can delay potential treatment in the setting of an already aggressive malignancy. This abstract is funded by: None