ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 PS-15-026 The frequency of EGFR mutations of non-small cell lung car- cinomas in the east Black Sea region of Turkey Z. Sagnak Yilmaz*, Z. Turkmen Usta, S. Aydin Mungan, S. Ersoz *Karadeniz Technical University, Faculty of Medicine, Pathology Department, Trabzon, Turkey Background & objectives: EGFR gene mutations are most common in exons 18-21. Exon 19 deletions and exon 21 L858R point mutation constitute 90% of them. We aimed to detect the frequency of EGFR gene mutations in the east Black Sea region of Turkey. Methods: We investigated the mutational status of 488 cases diag- nosed with non-small cell lung carcinomas between January 2019 and March 2022 with next-generation sequencing. QIAsec New Solid Custom MSI Panel was used. Results: We detected EGFR mutations in 10.2% of the cases (50 patients). It is mostly observed in exons 19, 20, and 21 which were 16 cases (32%) in exon 21, 15 cases (30%) in exon 19, and 12 cases (24%) in exon 20. In addition, EGFR mutations were detected in exon 15 in 7 cases (14%). Exon 19 deletions were seen in 14 cases (28%) and exon 21 L858R point mutations were seen in 10 cases (20%). Exon 20 T790M mutation, which causes tyrosine kinase inhibitor resistance, was observed in 3 of the cases. EGFR and TP53 co-mutations were detected in 8 patients. Conclusion: Consistent with the literature, the most frequently observed mutations were exon 19 deletions and exon 21 L858R mutation. Our results demonstrated the frequency of EGFR gene mutations in the east Black Sea region of Turkey. Although there are no clinical studies on exon 15 EGFR mutations in the literature, exon 15 mutations were detected in 14% of the cases in our study. This result may shed light on future studies. PS-15-027 Tumour PD-L1 expression and molecular profiling are not associated with immune checkpoint inhibitor-induced thyroid dysfunction in advanced non small cell lung cancer (NSCLC) Patients T. Neuman*, G. Vainer, A. Horesh *Hadassah-Hebrew university medical centre, Jerusalem, Israel Background & objectives: Immune-checkpoint-inhibitors (ICIs) has been revolutionary in treating advanced NSCLC, however- frequently associated with thyroid-related adverse events. We aimed to explore the association between patient characteristics, tumour PD-L1 expression and molecular profile with the development of thyroid dysfunction in these patients. Methods: Single centre, retrospective study assessing the asso- ciation between clinical parameters, tumour PD-L1 expression, molecular profiling, and the development of thyroid irAEs in 107 NSCLC patients treated with PD-1 or PD-L1 inhibitors from April 2016 to July 2020. All patients were euthyroid at baseline and had at least two TSH measurements post treatment initiation. Results: Overall, 37 (34.6%) patients developed any thyroid dysfunc- tion and 18 (16.8%) developed overt thyroid dysfunction. There was no association between PD-L1 staining intensity in the tumour and the development of thyroid dysfunction. TP53 mutation was less likely to be associated with the development of any thyroid dysfunction (p < 0.05). There was no association found between the development of thyroid dysfunction and EGFR, ROS, ALK or KRAS mutations. There was no association between PD-L1 expression and time to develop thyroid dysfunction. Conclusion: This study did not demonstrate an association between PD-L1 expression and the development of thyroid dysfunction in advanced NSCLC patients treated with PD-L1 or PD-1 inhibitors, suggesting that the thyroid-related adverse events are unrelated to PD-L1 expression in the tumour. PS-15-028 Identification of Maml1 as a novel negative regulator of Itch E3 ubiquitin ligase activity: new insights in cancer biology S. Zema*, M. Pelullo, A. Montalti, M. De Carolis, A. Villari, I. Screpanti, D. Bellavia *Sapienza University, Dept. of Molecular Medicine, Italy Background & objectives: Maml1 is a transcriptional coactivator in several pathways, such as Notch and Hedgehog, directly involved in the onset/development of several cancers. Here, we demonstrate that Maml1 can control the expression levels of Gli1 and Notch1 proteins at post-translational level. Methods: We utilized different experimental approaches: immuno- precipitation and ubiquitination assays in both in vitro and ex vivo (Maml1-/- murine model) cell lines; Maml1 silencing with CRISPR/ Cas9 technology; analysis of Itch post-translational modification; siRNA-mediated depletion of Maml1 in breast and colon cancer cell lines; wound healing assay; proliferation assays. Results: Gli1 and Notch1 are both regulated at post-translational level by Itch/E3 ubiquitin ligase. We demonstrate Maml1 capabil- ity to regulate Notch1 and Gli1 expression levels through Itch inhibition. For the first time, we identify the functional role of Maml1 C-terminal domain as a post-translational regulator of target proteins. Moreover, we pinpoint the molecular mecha- nism through which Maml1 acts as negative regulator of Itch, by inducing auto-ubiquitination events. Therefore, Maml1 increases the expression levels of Gli1 and Notch1 oncogenic proteins, by switching off Itch activity. Accordingly, in pathological con- texts, such as breast and colon cancers, Maml1 silencing impinge on Notch1 and Gli1 protein levels, hindering proliferation and epithelial-mesenchymal transition events. Conclusion: Overall, our data suggest a protective role mediated by Maml1 on Itch-target proteins involved in cancer biology. Indeed, the ability of Maml1 to negatively regulate Itch activity could have an impact in the activation of oncogenic pathways, such as Hedgehog and Notch. The identification of Maml1 as a novel negative regulator of Itch adds a piece in the understand- ing of tumour biology and could help to set out new therapeutic approaches based on the dual role of Maml1. PS-15-029 Characterising the cellular architecture of the tumour micro- environment using imaging mass cytometry and digital image analysis with the HALO® and HALO AI™ platform G. Lioux*, K. Collins, N. Carmell *Indica Labs, Inc., USA Background & objectives: The identification of biomarkers, and their spatial distribution in the tumour microenvironment (TME) can help establishing a prognosis and cure. Here we show the analysis of the TME using the HALO® and HALO AI™ platform in mass cytometry multiplexed images. Methods: Here, we present image analysis of more than eight different cancer types, such as bladder urothelial carcinoma, prostate adenocar- cinoma, and lung adenosquamous carcinoma, using the HALO and HALO AI software (Indica Labs, Inc.). Samples are formalin-fixed paraffin-embedded (FFPE) primary tumour biopsies prepared for imag- ing mass cytometry using Marpar® reagents from Fluidigm. Images were acquired with the Fluidigm Hyperion™ platform. S148