SESSION TITLE: Global Case Report Posters SESSION TYPE: Global Case Reports PRESENTED ON: 10/23/2019 09:45 AM - 10:45 AM INTRODUCTION: Pseudomesotheliomatous carcinoma is a rare type of lung adenocarcinoma (AD) that is characterized by growth in the pleural tissue of the chest cavity with clinical, radiological and even histological features similar to malignant mesothelioma. CASE PRESENTATION: A 47yo, never smoker, male doctor presented to our hospital with a 4-month history of left sided pleural pain. The past 15 years he lives and works in UK. On Christmas holidays, he visited his family and decided to undergo a plain CXR to see what this pleural pain was. CXR revealed a left pleural effusion. Thorax CT-scan demonstrated pleural fluid accumulation, pleural thickening areas and pleural nodules in the left hemithorax, as well as enlarged left hilar lymph nodes. A thoracentesis revealed an exudative. Analysis of two fluid samples reported benign characteristics and inflammation. A CT -guided FNB then was performed and a thoracic tube was placed to drain the hemithorax. A cytologic diagnosis of malignant cells was established based on new sambles of pleural fluid, possibly AD and IHC studies showed BerEP4(+), TTF1(+), CD56(-). Based on the results of the FNB, a histopathological diagnosis of pulmonary AD was made. Bronchoscopy and brain CT-scan were negative. The PET-CT scan demonstrated 18-FDG uptake by the pleural fluid, multiple nodules along the left pleura with possible infiltration of the diaphragm, peritoneal nodules and micronodules, nodular findings in the minor pelvis as well as by the left lobe of the thyroid gland. The CT-guided FNA of the thyroid gland was negative for malignancy. A new CT-guided FNB of the left pleura was performed and its histopathological analysis showed a well/moderately differentiated AD of the lung. Further IHC analysis revealed, TTF-1(+), CK7(+), CD15(+), EMA(+), BerEP4(+), Napsin-A(+), Calretinin(-), Thyroglobulin(-), Calcitonin(-), PAX-8(-), Chromogranin(-) and the fraction of Ki-67-positive tumor cells was 25%. Based on the clinical and laboratory findings the diagnosis of pseudomesotheliomatous type AD of the lung was made. To search for therapeutic strategies, additional gene detection was performed on the tissue sample, which showed no EGFR gene mutation (EGFRwt) but ALK rearrangement. The patient remains in excellent condition at the time of writing, under targeted therapy with alectinib. DISCUSSION: Pseudomesotheliomatous carcinomas most often are primary lung tumors but they can also be metastases from other sites. Adenocarcinoma of the lung is the most frequent type of malignancy that pseudomesotheliomatous carcinomas derive from as it also happened with our case. CONCLUSIONS: The treatment method for pseudomesotheliomatous tumors depends on the type and the origin of the given tumors with no specific guidelines published up to now and a poor prognosis is reported in most reviews in the literature. Our pt was ALK positive and it remains to see his clinical course with alectinib. Reference #1: Pseudomesotheliomatous’ carcinomas of the pleura: a 10-year analysis of cases from the Environmental Lung Disease Research Group, Cardiff R L Attanoos, A R Gibbs https://doi.org/10.1046/j.1365-2559.2003.01674.x Reference #2: Pseudomesotheliomatous carcinoma involving pleura and peritoneum: A clinicopathologic and immunohistochemical study of three cases. Shah IA1, Salvatore JR, Kummet T, Gani OS, Wheeler LA. Ann Diagn Pathol. 1999 Jun;3(3):148-59. Reference #3: Pseudomesotheliomatous lung carcinoma: a pathological assessment of selected cases including the work history and presence of biomarkers suggesting it is a cancer caused by asbestos. Samuel P. Hammar and Ronald F. Dodson. http://www.hoajonline.com/pathology/2052-7896/3/6 DISCLOSURES: No relevant relationships by Athanasios Andrianopoulos, source=Web Response No relevant relationships by Athanasia Athanasopoulou, source=Web Response No relevant relationships by Aikaterini Kavvada, source=Web Response No relevant relationships by Ilias Lyroudis, source=Web Response No relevant relationships by Asimina Nikolakopoulou, source=Web Response no disclosure on file for Georgios Noutsos; No relevant relationships by Emily Tsaroucha, source=Web Response No relevant relationships by Albanis Zannis, source=Web Response