UTILITY OF IMMUNOHISTOCHEMISTRY IN PLEURA-BASED LUNG CANCERS: A DIAGNOSTIC DILEMMA

Abstract

SESSION TITLE: Monday Medical Student/Resident Case Report Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: 10/21/2019 02:30 PM - 03:15 PM INTRODUCTION: Lung cancer screening guidelines do not target patients likely to develop cancers of the pleura, resulting in delayed diagnosis. Pleural lung cancers with clinicopathologic and histologic similarities such malignant melanomas (MM), sarcomatoid mesothelioma (SM) and synovial sarcoma (SS) further compound diagnostic uncertainty, resulting in increased morbidity and mortality, with 5-year survival rates as low as 9%. We present a case highlighting this diagnostic conundrum as well as the limitations of immunohistochemistry (IHC). CASE PRESENTATION: A 79-year-old male with history of atrial fibrillation on Eliquis, prostate cancer post brachytherapy and melanoma to the mid back post resection without sentinel lymph node biopsy presents to the ER with a 1 week history of progressive dyspnea on exertion and wheezing. He denied chest pain, palpitations, orthopnea, fever, constitutional symptoms or recent falls. He denied a history of radiation or asbestos exposure. On presentation vitals were normal with decreased breath sounds in the left middle to lower lung fields. Lab results were normal except mild anemia. Initial chest x-ray showed new large left pleural effusion. CT chest showed large left pleural effusion with multiple pleural-based nodules in the left upper lobe. Eliquis was held and two thoracenteses done days apart drained 2400cc of dark red exudative fluid, negative for malignant cells. A week later, video-assisted thoracoscopic surgery (VATS) was performed due to recurrent effusion. VATS revealed extensive lung pleura and pericardial studding; 1500cc of serosanguinous fluid was drained. Histology showed a malignant tumor composed of hyperchromatic spindle cells. Differentials included SS, MM and SM. IHC was positive for one of two melanoma markers (S100+, Melan-A-), one of two mesothelioma markers (WT1+, calretinin-), and also for TLE1 (synovial sarcoma marker). Repeat IHC at a large referral institution showed nonspecific staining for TLE1 and a final diagnosis of MM was rendered after comparison with previously resected MM. DISCUSSION: MM, SM and SS were considered in this case of recurrent bloody pleural effusions, multiple pleural-based plaques and spindle cell histology. MM and SM both carry poor prognosis compared with SS, necessitating definitive diagnosis. TLE1 was used as a specific marker for SS, but has been found in 69% of SM cases and 57% of spindle-cell melanomas. Molecular analysis for SYT-SSX can confirm SS, but is not always readily available. A definitive diagnosis was only made after comparison of previously resected melanoma, further illustrating the diagnostic dilemma. CONCLUSIONS: Lung cancer is the leading cause of cancer deaths in the USA with melanomas having the 6th highest incidence of cancers. Pleural lung cancers have the potential for high mortality with significant clinical and pathological overlap, for which IHC may not provide a definitive diagnosis. Reference #1: Matsuyama A, Hisaoka M, Iwasaki M, Iwashita M, Hisanaga S, Hashimoto H. TLE1 expression in malignant mesothelioma. Virchows Archiv. 2010;457(5):577-583. Reference #2: Morrell TJ, Xiong Y, Deng A, Dresser K, O’Donnell P, Cornejo KM. Expression of TLE1 in Malignant Melanoma with Spindle Cell Morphology: A Potential Diagnostic Pitfall. International Journal of Surgical Pathology. In press. https://doi.org/10.1177/1066896918805137. Reference #3: Lao I, Chen Q, Yu L, Wang J. Sarcomatoid malignant mesothelioma: a clinicopathologic and immunohistochemical analysis of 22 cases. Chinese Journal of Pathology. 2014;43(6):364-369. DISCLOSURES: No relevant relationships by Sahai Donaldson, source=Web Response No relevant relationships by Gene Otuonye, source=Web Response No relevant relationships by Dan Ran-Castillo, source=Web Response No relevant relationships by David Shiu, source=Web Response No relevant relationships by Matthew Tavares, source=Web Response No relevant relationships by Mikhail Tismenetsky, source=Web Response