ECP 2023 Abstracts

S20 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 tumour focus separately would not be cost-effective, the radiological-path- ological correlation would be the most appropriate approach to distinguish morphologically indeterminate cases. OFP-05-005 Endobronchial ultrasound guided transbronchial needle aspira- tion (EBUS-TBNA) and EBUS-guided transbronchial mediastinal cryobiopsy (EBUS-TMC) in the diagnosis of mediastinal lymphad- enopathy: our experience with the technique and proposal on its indication J. Martin Lopez*, G. Diaz Nuevo, E. Tejerina Gonzalez, D. Garcia Fresnadillo, C. Lopez García-Gallo, C. Salas Anton *Department of Pathology. Hospital U. Puerta de Hierro, Spain Background & objectives: EBUS-TBNA is the technique most fre- quently used in the study of mediastinal lymph nodes. In some cases, EBUS-TBNA fails to accurately diagnose (lymphoma-sarcoidosis) or obtains insufficient material to molecular testing (MT) and EBUS-TMC has proposed to resolve this situation. Methods: To evaluate the role of EBUS-TMC we present a case-series of eighteen patients from November 2022 to April 2023 who underwent EBUS-TBNA and TMC in a single procedure for diagnostic purposes of mediastinal lesions. Three cryobiopsies were performed per lymph node. All procedures were performed by the same two operators. Rapid onsite evaluation (ROSE) was done in all cases. Results: Of the cases, 2 cases were reactive lymphadenopathy with both techniques, 2 sarcoidosis, 2 SCLC and 12 NSCLC (3 SCC, 5 ADC, 2 TC and 2 NSCLC, NOS). In 2 cases a previous EBUS-TBNA was performed with a negative result and with the second procedure an SCLC and sar- coidosis was confirmed both in EBUS-TBNA and EBUS-TMC. In 2 cases EBUS-TMC confirmed a previous EBUS-TBNA diagnosis (2 cases of typi- cal carcinoid). EBUS-TMC got sufficient material toMT in 9 cases but also the EBUS-TBNA performed during the second procedure obtained enough in cell-block cytology (only 1 EBUS-TBNA was insufficient). EBUS- TBNA allowed the MT in one case that was insufficient with EBUS-TMC. Conclusion: EBUS-TMC following EBUS-TBNA reports a minimal increased of diagnostic yield than EBUS-TBNA alone. In our experi- ence, molecular testing in lung cancer was possible in most of the samples obtained from EBUS-TBNA. EBUS-TMC allowed us to iden- tify patients with sarcoidosis and perform PCR techniques for micro- organisms in cases with a previous EBUS-TBNA that was negative. We consider that the indication to perform EBUS-TMC should be in certain patients with previous insufficient EBUS-TBNA or selected in the setting of a multidisciplinary committee. OFP-05-006 Histological, immunohistological and molecular characterisation of congenital pulmonary airway malformation (CPAM) M. von Laffert*, S. Schweitzer, M. Lacher, O. Aubert, F.W. Hirsch, D. Gräfe, K. Hauptmann, A. Arnold, D. Horst, M. Chirica, F. Klauschen, U. Obeck, M. Boeschen, M. Stiller, H. Bläker *Institute of Pathology UKL University of Leipzig, Germany Background & objectives: CPAM is a hamartomatous cystic lesion of the lung. Possible histological findings are foci of goblet cell hyper- plasia (GCH),showing KRAS-mutations. Recently, KRAS-mutations were also described in the non-GCH regions. However, morphological studies, linking molecular data with immunohistochemistry (IHC) are scarce. Methods: We re-evaluated 39 cases (Stocker type I-III) and performed IHC (18 marker panel) with regards to cytokeratin expression, cell cycle, transcription factors (i.a. TTF1, PAX8, Napsin, Surfactant, CK5/6, CK7, CK20, p16, p53) and Next Generation Sequencing (NGS: 40 gene panel; 113 fusion genes panel). In samples with GCH, NGS was performed in cystic and non-cystic regions. Results: Type I was found in 28% (11/39), type II in 18% (7/39), type III in 3% (1/39). The majority of cases (51%) showed a mixed pattern (mainly type I and II). CPAM showed different expressions by means of CK5/6 (56% positive), Napsin (46% positive), Surfactant (44% positive) and CK20 (41% positive). Combined positivity of all 4 IHC-markers was only seen in 10% (4/39). 23% (9/39) showed KRAS mutations (7xG12D, 1xG12V, 1x G12D/V co-mutation). Mutations were detected in GCH and non-GCH cystic areas. One CPAM with KRAS G12D mutation had a further TP53 mutation. No fusions were detected. Conclusion: We were able to confirm recent data, showing that KRAS-mutations also occur in non-mucinous regions. To the best of our knowledge, we are the first group to report a KRAS G12D/ TP53 co-mutation and a CPAM harbouring a KRAS double mutation (G12D+V). Our preliminary data suggest a subclassification based on conventional histology, protein expression and molecular data (KRAS- status) to be more appropriate. The different expression patterns of CK5/6, Napsin, Surfactant and CK20 might reflect different stages during lung morphogenesis. OFP-05-007 National testing rate and prevalence of MET exon 14 skipping mutations in NSCLC in the Netherlands V.D. de Jager*, B. Cajiao Garcia, A.J. van der Wekken, L. van Kempen, E. Schuuring, S.M. Willems *Department of pathology and medical biology, University of Gronin- gen, University Medical Center Groningen, The Netherlands Background & objectives: Mesenchymal-epithelial transition ( MET ) exon 14 skipping mutations are uncommon, but targetable oncogenic alterations in non-small cell lung cancer (NSCLC). This study aimed to determine the testing rate and prevalence of these mutations in patients with metastatic NSCLC in the Netherlands. Methods: After linkage of clinical data of the Netherlands Cancer Registry (NCR) and pathology reports of the Dutch Pathology Registry (PALGA), molecular test status of MET exon 14 skipping mutations, molecular test type(s), and test outcome were manually extracted from pathology reports of patients diagnosed with metastatic non-squamous NSCLC between January 1st and December 31st 2019 in the Netherlands. Results: Among 3,803 patients included in this preliminary analysis, 71.9% received molecular testing for MET exon 14 skipping muta- tions within three months of diagnosis (2,734/3,803). Testing was not performed in 18.2% of cases (692/3,803) and MET testing status was unknown in 8.3% (316/3,803). Among MET -untested patients, 49.9% did not receive molecular testing for any predictive biomarker (345/692). In total, 47 patients had positive MET exon 14 skipping mutation test results, resulting in a prevalence of 1.7% in the MET -tested population (47/2,734). Among patients with confirmed EGFR / KRAS wt, 88.8% were simultane- ously or sequentially tested for MET (1,438/1,620). Conclusion: In the Netherlands, the predictive molecular testing rate for MET exon 14 skipping mutations in metastatic NSCLC was 71.9% in 2019. The prevalence of MET exon 14 skipping mutations was 1.7% in the MET -tested population. About half of all MET -untested patients did not receive molecular testing for any predictive biomarker, but the vast majority (88.8%) of patients with EGFR / KRAS wt did receive molecular testing for MET . Routine use of direct (i.e. non-sequential) next-generation sequencing (NGS) may increase the latter percentage. Funding: This work was supported by MSD, Pfizer, Astrazeneca, and Roche. The funders had no role in the design of the study, in the collec- tion, analyses, interpretation of data, or in the writing of the abstract (All fees transferred to UMCG account). OFP-05-008 Predicting the evolution of lung squamous cell carcinoma in situ using deep learning A. Vigdorovits*, G. Olteanu, O. Tica, M. Boros, O. Pop