ECP 2023 Abstracts

S84 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 PS-09-010 Clinicopathologic characteristics and succinate dehydrogenase deficiency in paragangliomas: a 10-year retrospective study from a tertiary care centre M.L. Sacramento*, E. Rios *Serviço de Anatomia Patológica, Centro Hospitalar Universitário de São João, Porto, Portugal Background & objectives: Paragangliomas are extra-adrenal neuroen- docrine tumours associated with underlying germline mutations in up to 80%, especially involving succinate dehydrogenase complex (SDHx) genes. SDHB immunohistochemistry (IHC) can predict SDHx muta- tions that have prognostic implications. This study aimed to characterize a paraganglioma series. Methods: A total of 36 paragangliomas were diagnosed retrospectively at our hospital over the last ten years (2012-2022). The clinical character- istics of the patients were collected, and all slides were reviewed. SDHB protein expression was examined on all tumours. Genetic results were available in 17 patients. Grading system for Adrenal Pheochromocytoma and Paraganglioma (GAPP) score was calculated whenever possible. Results: Among 36 cases, 26 were diagnosed in females (Male:Female = 1:2.6) . The median age at diagnosis was 48 years (range, 12–80 years). The most frequent location was the carotid body (13 cases). Tumour sizes were 0.4 to 11.6 cm (mean, 4 cm). SDHB expression loss occurred in 16 (44%) paragangliomas. Genetic study was available in 7 SDHB-deficient tumours: 6 SDHB mutations and 1 SDHD mutation. From these, 4 (in a total of 5) showed malignant behaviour. GAPP score was calculated in 17 tumours. In the well differentiated group (n=12), 4 were SDHB-deficient. In the moderately differentiated group (n=5), 2 were SDHB-deficient. Conclusion: Our study revealed a female predominance of paragan- gliomas and clinicopathologic characteristics that fit into the existing literature. SDHB-deficiency was observed in 80% of paraganglio- mas with malignant behaviour, highlighting that SDHB IHC can be regarded as a biomarker of prognosis in paragangliomas. A higher GAPP score correlates with malignant behaviour and syndromic back- ground, reinforcing that GAPP score is a useful tool for risk stratifica- tion in paragangliomas. PS-09-011 GATA3 and SF1 in silent gonadotroph tumours of the pituitary: do we really need both? J. Soukup*, H. Faistova, L. Gerykova, P. Poczos, T. Česák, M. Kosak, D. Netuka, F. Gabalec *University Hospital Hradec Kralove, Czech Republic Background & objectives: Detection of transcription factors is a cru- cial part pituitary neuroendocrine tumours (PitNETs) work-up. How- ever, SF1 antibodies can be costly and difficult to implement. Thus, we were interested in added value of detection of GATA3 for diagnosis of gonadotroph tumours. Methods: A total of 148 nonfunctional PitNETs diagnosed over 15-year period were analysed for immunohistochemical expression of Pit1, Tpit, SF1 and GATA3. In selected cases, additional pituitary hormones, and cytokeratin 8/18 were evaluated. Results: The cohort consisted of 120 (81.6%) gonadotroph PitNETs, 14 (9.5%) corticotroph PitNETs, 9 (6.1%) Pit1+ PitNETs, 3 (2%) null-cell tumours and 1 (0.7%) plurihormonal PitNETs. Pit1-lineage tumours were exclusively Pit1-positive. Among ACTH+/Tpit+ corticotroph Pit- NETs, 3 out of 14 demonstrated weak GATA3 positivity. Among 120 gonadotroph tumours, 105 (87.5%) were GATA3+/SF1+; 10 tumours were GATA3+ (8.3%) and only 5 (4.2%) were SF1+. GATA3 exhib- ited 95.8% sensitivity and 85.7% specificity for diagnosis of gonado- troph PitNET, while SF1 showed lower sensitivity (91.7%) but higher specificity (96.4%). The use of Pit1/Tpit/GATA3 panel resulted in diagnosis of 8 (5.4%) null cell tumours, compared to 13 (8.8%) null cell tumours identified by Pit1/Tpit/SF1 panel. Conclusion: GATA3 is a more sensitive marker of gonadotroph PitNETs compared to SF1. Applying a Pit1/Tpit/GATA3 panel led to a misdiagnosis of 3.4% of PitNETs as null-cell tumours, while a Pit1/Tpit/SF1 panel resulted in a 6.8% misdiagnosis rate. However, GATA3 immunoreactivity was observed in a subset of corticotroph tumours, and it can be also present in a subset of Pit1+ tumours with thyrotroph differentiation. Thus, it should be always included with additional PitNET lineage markers (at least Pit1 and Tpit). Funding: BBMRI-CZ LM2023033; Charles University Cooperatio Program DIAG and METD; Czech Ministry of Defense MO 1012; European Regional Development Fund-Project BBMRI-CZ Biobank network – a versatile platform for the research of the etiopathogenesis of diseases, No: EF16_013/0001674 PS-09-012 A prognostic marker panel (OTP, CD44, Ki-67) predicts relapse free survival in patients with surgically resected pulmonary carcinoid E.J. Speel*, L. Moonen, J. Derks, M. Den Bakker, L. Hillen, J. von der Thüsen, R.J. van Suylen, R. Damhuis, K. Smits, W. Buikhuizen, G. PALGA, A. Dingemans *Maastricht UMC, The Netherlands Background & objectives: Relapse occurs in 10% of patients with resected pulmonary carcinoid (PC). Aim was to examine if an immu- nohistochemical (IHC) marker panel (OTP, CD44, Ki-67) improves 1) uniformity among pathologists (compared with WHO classification) and 2) prediction of relapse-free survival (RFS). Methods: All surgically resected PC (2003-2012) were identified from the Dutch cancer/pathology registry. A case-control cohort (2:1 for relapse, N=170) was established. 4 pathologists independently revised cases and assessed IHC-markers (OTP&CD44 H-score, Ki-67 eyeball). IHC cut-off values were determined using ROC curves. Agreement between pathologists for classification and IHC was determined using kappa. The remaining total cohort (N=396/566) was scored similarly. Results: Median FU of 2:1 cohort was 86.7 months and 61% (n=35/57) of relapsed patients had TC diagnosis. Revision showed poor kappa among pathologists (necrosis:0.48; mitotic count:0.38), whereas IHC markers showed high kappa (OTP:0.98, CD44:0.98, Ki-67:0.92). ROC analysis for relapse identified optimal cut-off for OTP (<50), CD44 (<30), and Ki-67 (≥5). Mean negative predictive value (NPV) for relapse increased from 0.74 (TC diagnosis) to 0.85 (IHC low-risk [OTP≥50 & CD44≥30 & Ki-67<5]). IHC risk stratification of total cohort (high-risk [n=220] and low-risk [n=314]) showed a NPV of 96%. Conclusion: Our study shows that the IHC marker panel including OTP, CD44, and Ki67 increases diagnostic uniformity among patholo- gists and reveals a high NPV (96%) for relapse, indicating that a bio- marker driven FU management for PC patients may be used to identify patients who can be excluded from long-term FU. Further studies are warranted to validate our findings, also in the light of the recently identified clinically relevant molecular PC subtypes. Funding: Dutch Cancer Society PS-09-013 Mature fat containing thyroid lesions: report of five cases A. Yavuz*, B. Altunay, E. Ocak Gedik, C. Arıcı, G.A. Ocak, I.E. Gurer *Akdeniz University Department of Pathology, Turkey Background & objectives: The thyroid gland does not normally consist adipose tissue. Rarely, non-neoplastic and neoplastic thyroid