ECP 2023 Abstracts

S26 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 H-score for EBVNPC was 180 (range 12-295; mean 179), whereas the median H-scores for HPVSCC and VNSCC were 0 (range 0-56; mean 8) and 0 (range 0-125; mean 31), respectively (p<0.001 for EBVNPC compared to either). Conclusion: Our study validates the strong correlation between SSTR2 immunohistochemistry and EBV status in NPCs, supports its use in clinical practice as a highly sensitive and specific surrogate biomarker, and lends credence to exploring SSTR2-targeted imaging and therapy. The study does not have its own funding. However, the research was supported in part by the Cancer Tissue and Pathology shared resource of Winship Cancer Institute of Emory University and NIH/NCI under award number P30CA138292. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. OFP-06-011 Mapping viral integration sites in human papillomavirus positive head and neck squamous cell carcinomas using proximity ligation- based sequencing E.J. Speel*, I. Demers, H. Balaji, N. Wuerdemann, S. Wagner, B. Kremer, C. Huebbers, J. Klussmann *Maastricht UMC, The Netherlands Background & objectives: Human papillomavirus (HPV) integration may affect HNSCC carcinogenesis and prognosis. Study aim was to assess HPV integration in HPV-positive HNSCC cell lines and FFPE tissue comparing the new Targeted Locus Amplification (TLA) tech- nology with previously used PCR technology (APOT/DIPS). Methods: Seven HPV-positive cell lines and FFPE material of 27 HPV- positive HNSCCs were used for HPV integration detection by TLA, a prox- imity ligation-based NGS technique. Crosslinked DNA is digested with restriction enzymes, and re-ligated into chimeric DNAmolecules. For cell lines a PCR-based and for FFPEmaterial a capture-based target enrichment was performed for HPV16 sequences, followed by Illumina sequencing. Results: TLA was able to sequence up to 100 kb around the target, detecting exact HPV integration loci, structural variants, and chromo- somal rearrangements. In all cell lines, one or more integration sites were identified, in accordance with APOT/DIPS PCR data and the lit- erature. In the FFPE tissue samples, TLA identified integrated HPV in 15 out of 27 tumours, with simple and more complex integration patterns, confirmed by qPCR data. TLA confirmed known PCR data, identified additional integration sites, and proved useful in establishing clonal relationships of multiple tumours within a patient. Conclusion: TLA provides the opportunity for reliable and robust detection of HPV integration in HNSCC cell lines and FFPE tis- sue. This new sequencing technology will be a useful tool for further research on HPV integration in disease and patient outcome and clonal- ity analysis of multiple tumours within a patient. OFP-06-012 Molecular profiling and classification of odontogenic lesions S.E. Gultekin*, B. Tokozlu, C. Heydt, R. Aziz-Heiloun, O. Gunhan, R. Buettner *Gazi University, Faculty of Dentistry, Turkey Background & objectives: Odontogenic tumours (OTs) comprise a group of heterogeneous lesions. There are various types of OTs and still different views exist as to their correct classification. Therefore, we here performed comprehensive molecular profiling of odontogenic lesions, to identify genomic alterations. Methods: We analysed a cohort of 70 odontogenic lesions with cysts and benign or malignant tumours. NGS was performed with an in- house specified, customized hybrid capture-based primer panel of 31 different genes. Mutational patterns were compared with histological diagnosis for each entity. The correlation of genomic profiles with clas- sification of the tumours and clinical parameters (age, gender, location, recurrence) was statistically analysed. Results: Mutations were identified in 46 of 70 available odontogenic lesions (66.7%) while 23 lesions were classified as wild-type. Odonto- genic epithelial tumours significantly harboured more mutations than mixed or mesenchymal types (p=0.008). In malignant tumours, muta- tions were observed in 75% of cases which was statistically significant (p=0.05). Among our 46 cases with mutations, 11 cases harboured two simultaneous genetic alterations. With respect to KRAS, the c.35G>T p.G12Vs mutation was the most prevalent alteration detected in 14 and 12 cases, respectively. The PATCHED-1 mutation, which was the third most common mutation, was exclusively detected in 9 out of 10 OKC cases (90%) (p≤0.000). Conclusion: Our data strongly suggest that histological classification and mutational status in OTs consistently coincide and that obtain- ing the mutational status may facilitate histological typing in difficult incisional biopsies. OFP-07 | Oral Free Paper Session Dermatopathology OFP-07-001 Epidermal ELAFIN expression for diagnosis and differentiation of acute cutaneous graft-versus-host disease E. Kuzucular*, F. Özden *Istanbul Medipol University, Turkey Background & objectives: Graft versus host disease (GVHD) is a severe complication observed following approximately 40-60% of allogeneic hematopoietic stem cell transplants. We aimed to evaluate the utility of elafin expression in skin by immunohistochemistry for accurate diagnosis of acute skin GvHD. Methods: We performed the histological examination of biopsy samples from acute GvHD (aGvHD; n = 69), Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN; n = 18), drug reaction (DR; n = 31), and healthy controls (n = 23). Elafin was applied immunohistochemically and staining of ≥ 50% of the epidermis was considered positive. Results: In total, 141 patients were included in the study. In aGVHD cases, 56/69 biopsies, elafin positivity was observed; in only 13 cases, expression was not seen. SJS/TEN patients, with 6/18 biopsies focally showing 50% positivity. In 11 samples, elafin expression was found only in single cells; one biopsy was negative. In DR patients, 2/31 biopsies exhibited 50% staining in some parts of the epidermis; 15 showed staining only single cells in the granular layer; 14 were negative. Twenty-three healthy control biopsies were entirely elafin negative; in four samples, only single cells in the granular layer were stained. Conclusion: Specific markers cannot exclude clinical mimics of acute skin GVHD (such as drug reaction and SJS/TEN). It is difficult to distinguish between clinical mimics based on histopathology alone because they may present with similar clinical/histological symptoms. We conclude that elafin has a high rate of positivity in aGVHD cases. Tissue elafin is a useful immunohistochemical marker for acute skin GVHD. However, more extensive studies are needed to validate these results. OFP-07-002 Overexpression of MicroRNAs 21 and 199 related to the synthesis of collagen V in patients with keloid scars V. Berton Liguori Zacchi*, A. Sousa Santos, L. Henrique Gomes Matheus, T. de Matos Lobo, Z.A. de Jesus Queiroz, C. Machado Bal- davira, V. Elias Contini, S. de Morais Fernezlian, A.P. Pereira Velosa, V.L. Capelozzi, W. Rosolia Teodoro *Division of Rheumatology, Faculdade de Medicina da Universidade de São Paulo, Brazil