ECP 2023 Abstracts

S83 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 without were pT1 and 16.3% vs. 24.4% were pT2. Similar rate of pT3 and pT4 was present. Conclusion: Papillary thyroid carcinoma with FND was related to a diagnosis in older patients and a more indolent course, documented by a lower rate of extra-thyroidal extension, metastization to local lymph nodes and a lower staging (higher rate of pT1 staging vs lower rate of pT2) when compared to PTC alone. PS-09-007 Identification of NIFTP-specific mRNAmarkers for reliable molecular diagnosis of thyroid tumours C.K. Jung*, S. Lee, J. Park, K. Kim, J.S. Bae, S. Kim *Department of Hospital Pathology, College of Medicine, The Catholic University of Korea, Cancer Research Institute, College of Medicine, The Catholic University of Korea, Republic of Korea Background & objectives: Distinguishing non-invasive follicular thy- roid neoplasm with papillary-like nuclear features (NIFTP) from other thyroid tumours can pose diagnostic challenges, even with molecular testing. This study aimed to identify NIFTP-specific mRNA markers for improved diagnostic accuracy. Methods: Using RNA sequencing analysis of fresh thyroid tumour tissues from 74 cases, we identified differentially expressed genes and pathways in NIFTP/malignancy compared to benign tumours. We utilized Venn diagrams to identify significantly further dysregulated mRNAs in NIFTP. We selected mRNA markers using the Akaike infor- mation criterion (AIC) analysis and performed receiver operating char- acteristic analysis to estimate their accuracy. Results: Our analysis revealed 255 downregulated and 737 upregu- lated genes in NIFTP/malignancy compared to benign tumours. KEGG pathway enrichment analysis further showed several cancer-associated pathways in NIFTP/malignancy. Using Venn diagrams, we identified 19 significantly upregulated and 7 downregulated mRNAs in NIFTP. After validating our results in The Cancer Genome Atlas (TCGA) dataset, we selected OCLN, ZNF423, LYG1, and AQP5 mRNA markers using AIC analysis and developed a prediction model that exhibited good accuracy in predicting NIFTP in both our cohort and the TCGA cohort. Conclusion: Our study suggests that the identified four mRNA markers can serve as reliable molecular markers for identifying NIFTP among other thyroid tumours, thus aiding in the accurate diagnosis and man- agement of NIFTP patients. This research was supported by “Systemic Industrial Infrastruc- ture Projects” through the Ministry of Trade, Industry, and Energy (MOTIE) (P0009796, 2019) and the KRIBB Research Initiative Pro- gram (KGM5192322). This research was also supported by a grant (HI21C0940) from the Korean Health Technology R&D Project, Min- istry of Health and Welfare, and a grant (NRF-2020R1F1A1070028) from the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science and ICT. PS-09-008 A comprehensive clinico-pathological study of carcinoma and atypical adenomas from parathyroid in a series of patients with long-term follow-up J. Machuca Aguado*, P. Rodríguez de Vera Gómez, Á. Gutiérrez, T. Martín Hernández, J.J. Rios Martin, M.A. Idoate Gastearena *Virgen Macarena University Hospital, Seville, Spain Background & objectives: Parathyroid carcinomas (PC) are rare neo- plasms with histopathological differences from atypical parathyroid adenomas (APA), with a rather similar clinical course, excepting the very unusual PC metastases. Our aim was to identify variables for a better characterisation of both tumour types. Methods: It is a retrospective observational clinicopathological study of a series of 7 PC and 10 APA which were diagnosed according to the WHO 2022 criteria with a median follow-up of 11 years. Immunohis- tochemistry was performed for parafibromin, PGP 9.5 and galectin 3. Post-surgical tumour recurrence was determined using clinical imaging and/or by elevation of parathormone (PTH) in blood. Results: No statistically significant differences were observed between PC and APA in terms of age, sex, pre-surgical blood tests (PTH and calcaemia), ultrasound characteristics, percentage of post-surgical cure and tumour recurrence (29% vs 20%; p=0.63). No metastases were identified. Immunohistochemically, no differences in parafibro- min, PGP 9.5 or galectin-3 expression were observed between PC and APA. Tumours with loss of parafibromin expression (5/17, 29.4%), 2 APA and 3 PC, were associated with older age (74 years vs 54 years, p=0.04), negative PGP 9.5 expression (80% vs 16%, p=0.02), infiltra- tion of adjacent structures (60% vs 33.3%, p=0.05) and capsular inva- sion (100% vs 58.3%, p=0.06) Conclusion: It can be concluded that no analytical or clinical behav- ioural differences were observed between PC and APA. Furthermore, no metastatic PC were found in a systematic follow-up under close scrutiny. Interestingly, parathyroid tumours with loss of parafibromin showed locally more aggressive behaviour and should therefore under- take continuous clinical monitoring. PS-09-009 Prognostic impact of fibrosclerotic changes in (non-papillary) fol- licular cell-derived thyroid carcinomas G. Orlando*, G. Capella, E. Vissio, G. Trucco, J. Metovic, F. Maletta, M. Volante, M. Papotti *Pathology Unit, Department of Oncology, University of Turin, Italy Background & objectives: Prognostic factors in thyroid carcinomas, with special reference to non-papillary histotypes, are scarce. Intratu- moral fibrosis was identified as an adverse prognostic factor in papillary carcinomas but has not been investigated in other subtypes, including follicular, oncocytic and poorly differentiated carcinomas. Methods: The presence of intratumoral fibrosis and its correlation with clinical outcome was analysed in 132 non-papillary follicular cell- derived thyroid carcinomas (53 follicular carcinomas, 31 oncocytic carcinomas and 48 poorly differentiated carcinomas). The percentage of fibrosis x tumour area was assessed on Hematoxylin & Eosin slides by two independent pathologists and, in 65 selected cases, using digital image analysis. Results: Spearman’s correlation agreement between the two observ- ers and with digital image quantification was very high (p<0.0001). The presence of intratumoral fibrosis (scored as absent, mild if <10% or extensive if >10%) was significantly associated with poorly dif- ferentiated carcinoma histology, large tumour size, extensive vascular invasion, presence of necrosis, high mitotic index, positive nodal status and aggressive clinical outcome (all p<0.01). Moreover, fibrosclerotic changes, either mild or extensive, were associated in the whole series with a significantly shorter disease-free and disease-specific survival (p<0.0001 in Log Rank test), retaining statistical significance also in differentiated (follicular and oncocytic) and poorly differentiated car- cinomas analysed separately. Conclusion: Intratumoral fibrosis is a potential novel prognostic factor in non-papillary follicular cell-derived thyroid carcinomas. It is associ- ated significantly with the presence of parameters of aggressiveness, and with a decreased survival rate independently from the tumour histotype. It is also easily assessable, with a very high interobserver agreement, thus supporting its potential use in the clinical diagnostic practice.