ECP 2023 Abstracts

S344 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 been well described in various organ systems under several names, most recently, “high-grade neuroendocrine carcinoma with carcinoid morphology”. No consensus on the best term for this tumour in the pul- monary pathology literature. It remains listed as a variant of LCNEC in the current WHO classification for lung and thymic tumours. Conclusion: The clinical experience with this rare tumour is obviously limited in the literature, but data suggests that it may be more closely related to atypical carcinoid tumours rather than LCNEC (at least from a molecular genetic standpoint). Clinically, there is data suggesting that it may not be as highly aggressive as conventional LCNEC, but it should be noted that this patient’s tumour has clearly declared itself as a “bad actor” showing aggressive behaviour and hence should be treated accordingly. E-PS-21-025 Multiple lung tumours with identical morphology. Synchronous primaries or intrapulmonary metastasis? A. Lazim*, A. Arriola, M. Mollaee *Temple University Hospital, USA Background & objectives: The incidence of synchronous multiple primary lung cancers (SMPLC) have been increasing with an estimate of 2%. Tumours with identical morphology remains a challenge to be classified. Methods: Distinguishing SMPLC from a primary tumour with intrapulmonary metastasis is very important for the clinical manage- ment as the response of different tumours to therapy is different. Here we report a case of an 84-year-old female found to have two discrete, synchronous lung masses bilaterally on imaging studies. Results: The patient underwent wedge resection and segmentectomy of the tumours within 4 months interval. The 1.9 cm right upper lobe showed invasive adenocarcinoma, acinar predominant with focal vis- ceral pleural invasion. PD- L1 reported strong expression (70%). No mutation was identified on targeted next generation sequencing (NGS). The opposite side wedge resection for the second tumour was per- formed 4 months after. The 1.7 cm left upper lobe tumour showed inva- sive adenocarcinoma, acinar predominant. The tumour had no expres- sion of PD- L1 and NGS analysis demonstrated only TP53 mutation. Conclusion: Following institutional multidisciplinary discussion, based on different molecular genetic characteristics, the decision was made to treat the patient’s tumours as synchronous multiple primary lung cancers rather than intrapulmonary metastasis. In clinical practice, it is difficult to distinguish synchronous multiple primary lung cancers from intrapulmonary metastasis especially when the tumours have identical morphology. Hence, advancement of biomarker testing, and next generation sequencing and application of these tools combined with histopathological analysis will improve the clinical management and outcome of these patients significantly. E-PS-21-026 Adenomyomatous Pulmonary Hamartoma with mucinous differ- entiation: avoiding subclassifications J.d.B. Machuca Aguado*, A. Álvarez-Muñoz, E. Rodríguez-Zarco, S. Umbría-Jiménez, J.J. Rios Martin, A. García-Escudero *Virgen Macarena University Hospital, Seville, Spain Background & objectives: Recently, a rare variant of pulmonary hamartoma has been described, characterised by a leiomyomatous stroma and glandular structures of different types. Rossi et al. published 6 cases in 2021 involving mucinous epithelium and found 5 additional cases in the literature. Methods: Retrospective observational clinicopathological study of a series of 3 cases of pulmonary adenomyomatous hamartoma. Clin- icopathological features were described and immunohistochemical analysis was performed, evaluated by three independent pathologists. Results: We described the morphological features of a biphasic lesion with a stromal component consisting of smooth muscle tissue and a glandular component. We identified three types of glands: several small glands covered by cells with round nuclei and scarce cytoplasm; branching epithelial clefts; and a third type covered by an epithelium with a broad mucinous cytoplasm, with mucoid content. This last type was only present in two of the cases, and they did not express TTF1 nor did it present p63 expression because it lacked a row of basal cells, unlike the first two types of glands. With Ki67, we observed a low proliferation index in all components. Conclusion: Unlike many of the cases published, the glandular com- ponent of our patients was not exclusively mucinous. Therefore, we believe that these lesions should be included in the same category. We propose a broader generic term for all these lesions to avoid confu- sion in the terminology by overly extensive subclassifications. The term “adenomyomatous pulmonary hamartoma” seems appropriate, specifying, when appropriate, mucinous differentiation. The biphasic appearance and the mucinous glands may result in diagnostic problems if pathologists are unaware of this entity. E-PS-21-027 Mass-forming pulmonary crystal-storing histiocytosis with medias- tinal lymph node involvement: a case report and literature review E. McGrath*, G. Heuston, R. Shatwan *St Vincent’s University Hospital, Dublin, Ireland Background & objectives: Crystal-storing histiocytosis is an extremely rare manifestation of underlying lymphoproliferative disorders that pre- sents as an accumulation of histiocytes with abnormal intra-lysosomal deposition of immunoglobulin light chains as crystals of unknown aeti- ology. Deposition can occur in a number or organ systems. Methods: Case report: we report a case of a 58-year-old male who underwent surgical resection of multiple pulmonary nodules of crystal- storing histiocytosis with mediastinal lymph node involvement and with no associated lymphoproliferative disorder. Results: After presenting with multiple episodes of shortness of breath, a CT scan showed mediastinal lymphadenopathy with slowly enlarg- ing right upper lobe nodules and ground glass opacities, one of which showed low grade PET positivity. An elective right upper lobectomy and lymph node dissection were carried out. Histology showed mul- tiple well-formed nodules of crystal storing histiocytosis which were positive for CD68 and kappa and lambda light chains on immunohis- tochemistry. Other markers including AE1/3, CD1a, desmin, myo-D1, HMB45 and S100 were negative. The patient was not found to have any lymphoproliferative disorder after extensive haematological work up. Conclusion: We report a case of nodular pulmonary crystal-storing histiocytosis involving the right upper lobe and ipsilateral hilar lymph nodes in a patient with no history of lymphoproliferative disorder. The main differential diagnosis for mass-forming crystal storing histiocy- tosis is pulmonary malignancy and this may cause diagnostic chal- lenges on both imaging and histology. It is therefore an important, albeit extremely rare differential diagnosis to consider. E-PS-21-028 A rare case of NSCLC with TTF1 and p40 coexpression - a new subtype to consider? O.F. Mülkem*, E. Tekin, M.C. Sivrikoz *Eskişehir Osmangazi University, Faculty of Medicine, Department of Pathology, Turkey Background & objectives: Lung cancer is currently the leading cause of cancer-related deaths worldwide. The treatment of lung cancer has been determined by the histological classification and stage. The coexpression of TTF1 and p40 within the same tumour cells is an exceedingly rare.