ECP 2023 Abstracts

S72 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Conclusion: The presence of CTNNB1 was a common finding in the BCAs of our sample, which is consistent with the current literature. Membranous BCAs lack biphasic cellular pattern, nuclear β-catenin expression and CTNNB1 mutations in contrast to other morphologic subtypes of BCA. PS-04-009 Determination of vimentin 3 (Vim3) and miR-15a expression profile in ameloblastomas: a preliminary study S.E. Gultekin*, H. Goebel, E. Baris, B. Koditz, İ. Atak Secen, M. Freifrau von Brandenstein *Gazi University Faculty of Dentistry, Turkey Background & objectives: Ameloblastoma is a mostly benign but locally aggressive odontogenic tumour. Vim3 was defined as a different protein with a unique C-terminal ending and proposed as a differential marker for kidney tumours. We aimed to determine Vim3 expression profile in ameloblastomas. Methods: The study was conducted immunohistochemically on a total of 45 paraffin-embedded tissue samples including conventional amelo- blastoma (n:15), unicystic (n:15) and dental follicle as control (n: 15). The expression of Vim3 and Full - length (FL-vimentin) and related miRs (mir 498 and mir 15a) was detected by using immunohistochem- istry and q RT- PCR. Results: The positive staining with Vim3 was seen in parenchymal cells (ameloblastoma-like cells) whereas FL- vimentin was solely posi- tive in the stroma. The tumour cells were not stained by FL- vimentin. A significant, increase of Vim3 (p<0.05) and mir 15a (p<0.0001) and a slight increase of mir 498 in the samples of conventional ameloblas- toma cases were detected compared to unicystic and controls. Conclusion: Here, we identified the first time Vim 3 expression in ameloblastomas which is structurally and functionally different from full-length (FL) vimentin. Our preliminary data displayed the expres- sion pattern of Vim3 in ameloblastomas which may have the potential to be used as a biomarker in the future. Funding: The Scientific and Technological Research Council of Türkiye (TÜBİTAK) and German Academic Exchange Service (DAAD) Bilat- eral Cooperation Travel Support Program PS-04-010 Multiple primary carcinoma in the oral cavitiy: new insights into clinicopathological and molecular characteristics A.B. Larqué Daza*, J. de la Oliva, P. Jares, P. Castillo, G. Frigola, C. Marti, A. Ferrer, E. Garcia, L. Alos *Hospital Clínic of Barcelona, Spain Background & objectives: The development of multiple primary carcinomas in the oral cavity is attributed to the field cancerization phenomenon. The objective of this study was to determine similarities or differences in gene mutations between the primary (index) tumours and the subsequent lesions. Methods: A retrospective pathology database search was performed to identify all oral squamous cell carcinomas diagnosed at our institution from the last 15 years. Patients’ demographics, clinical history, and microscopic findings were reviewed to identify multiples primary oral carcinomas. Eight samples corresponding to four index tumours, two second primary tumours and two recurrences were sequenced by next generation sequencing. Results: 501 patients were diagnosed with oral squamous cell carcino- mas in our hospital. Among these, 43 patients (8.6%) developed two or more primary tumours. Multiple primary tumours frequently affected older women and appeared preferentially in the tongue. The next gen- eration sequencing panel showed a totally different molecular profile between the first tumours (index tumours) and second primary tumours, whereas common molecular alterations, consistent with clonality, were found in the index tumours and their tumour recurrences. Moreover, three separate TP53 mutations was found in a recurrent tumour. Conclusion: In conclusion, the development of multiple primary tumours in the oral cavity is a frequent event that occurs predomi- nantly in older women. The next generation sequencing cancer panels can be useful to differentiate second primary tumours from tumoral recurrences. The finding of three separate TP53 mutations in one of the recurrence tumour could suggest that it is a recurrent polyclonal tumour. PS-04-011 Primary osteosarcoma of the mandible: a report of seven cases W. Majdoub*, K. Ben Lazreg, S. Mestiri, A. Baccouche, L. Jaidane, D. Benletaifa, M. Krifa, A. Bdioui, S. Hmissa *Pathology Department Sahloul Hospital, Tunisia Background & objectives: Osteosarcomas account for 40-60% of pri- mary malignant bone tumours and can arise in any bone. The localiza- tion in the mandibula is extremely rare. We aim to provide a clinico- pathological description of 7 cases of osteosarcoma of the mandibule (MOS). Methods: We conduct a retrospective study of 7 patients diagnosed with MOS listed in the Cancer Registry of Center Tunisia during a period of 15 years from 2006 to 2021. MOS were diagnosed on biopsy or on hemimandibulectomy specimen. Results: The mean age was 46 years with extremes of 16 and 87 ans. There were 4 females and 3 males. All tumours have an osteolytic aspect on imaging consistent with malignancy. Two cases were diagnosed on biopsy and five cases on hemimandibulectomy specimen. The tumour was localized in the mandibular body in three cases and in the horizontal branch in four cases. Median size was 4.7 cm and ranged from 3 to 7.5 cm. All tumours were of high grade with a chondroblastic osteosar- coma in two cases and an osteoblastic chondrosarcoma in four cases. Chemotherapy was administrated in 6 cases and radiotherapy in a case. Conclusion: Osteosarcoma has a large histomorphological spectrum and can be classified into 3 groups: low-grade (paraosteal or central), inter- mediate grade (periosteal) and high grade (conventional, telangiectasic and small cell). The conventional subgroup includes osteoblastic, chon- droblastic and fibroblastic osteosarcoma. There is no specific tumour classification system for MOS. Two common misdiagnoses are benign tumours and chondrosarcomas on biopsy samples. Immunohistochem- istry lacks diagnostic specificity but might be helpful in some cases. The prognosis is poor and deaths are frequently due to local relapse. PS-04-012 PD-L1 immunohistochemistry in head and neck squamous cell carcinoma: an audit of positivity rates and turnaround times at a referral centre in the United Kingdom K. Moutasim*, B. Templer *University Hospital Southampton, United Kingdom Background & objectives: PD-L1 immunohistochemistry is employed to identify patients that might respond to anti-PD1 immunotherapy. The principal aim of this audit was to compare the positivity rates at a large referral centre (University Hospital Southampton) with those in published clinical trials. Methods: This was a retrospective audit of hospital records of 100 PD-L1 cases (2021-2022), that had been stained with the 22C3 PharmDx Dako antibody. Scoring was performed using the com- bined positive score (CPS). Turnaround times of test results were also recorded, in addition to histopathological data from individual tumours. Results: Over 90% of cases tested had a CPS of 1 or more and were therefore regarded as being positive. The remaining cases had a CPS of <1 and were regarded as negative. These ’real life’ data are