ECP 2023 Abstracts

S282 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 E-PS-11-047 Clinical and pathological features that predict double-hit lym- phoma: a systematic review and meta-analysis K. Wong*, E. Lee*, H.C.J. Yang, E. Soilleux *Department of Pathology, University of Cambridge, United Kingdom Background & objectives: Differentiating double-hit lymphoma (DHL) from other high-grade B-cell lymphomas (HGBCL) is crucial, as DHL patients require more intensive treatment. We aimed to identify clinicopathological, morphological and immunohistochemical features predicting DHL, as alternatives to more expensive and inaccessible fluorescence in-situ hybridisation. Methods: We conducted a PRISMA systematic review and meta- analysis on 27 studies comparing the clinicopathological features between double-hit and non-double-hit HGBCL patients using four databases. Data on study characteristics, patient demographics, and clinicopathological, morphological and cytogenetic features of the lymphomas were extracted and risk ratios were calculated between DHL and HGBCL, and between MYC/BCL2-rearranged and MYC/ BCL6-rearranged DHL. Results: Our literature search yielded 771 DHL and 1551 HGBCL patients. DHL patients were more likely than HGBCL patients to have higher Ann Arbor stage and IPI score, elevated lactate dehydrogenase, bone marrow involvement, GCB immunophenotype (RR 1.2723, p=0.0361) and MYC immunohistochemical expression (RR=1.1106, p=0.0272); extranodal disease and B symptoms were more common in DHL, albeit not at a level reaching statistical significance. Further- more, MYC/BCL6-rearranged compared to MYC/BCL2-rearranged DHL patients were more likely to present with extranodal disease and central nervous system involvement and to show BCL2 immunopositiv- ity (RR 0.4062, p=0.0251); MYC immunopositivity was slightly more common in MYC/BCL6-rearranged lymphoma although this did not reach statistical significance. Conclusion: Our meta-analysis has identified MYC immunohisto- chemical expression and GCB immunophenotype as histopathological features that strongly predict DHL. Our results support their inclusion in selection criteria for stratifying potential DHL for confirmation with FISH, an important finding as there is no consensus on which histo- pathological features should be included. Investigations with larger sample sizes and establishment of detection thresholds will be essential to determine whether further immunohistochemical or immunopheno- typic markers, such as BCL2 immunopositivity, can potentially expand the selection criteria. E-PS-11-048 Megakaryocyte size in myeloproliferative neoplasms and myelod- ysplastic syndromes measured with digital pathology J.T. Zuñiga Gaitan*, C.E. Haro Haro, Z. Calixto Alvarez, J. Chabla Jaramillo, S. Ramón y Cajal Agüeras, J. Castellvi Vives *Vall D’ Hebron University Hospital, Spain Background & objectives: Megakaryocytes size and number are fre- quently used as a morphological criterion for the diagnosis of Myelo- proliferative Neoplasms (MPN) and Myelodysplastic Syndromes (MDS) in bone marrow biopsies. However, there are no objective standardized measures. Digital evaluation of megakaryocytes was performed. Methods: We selected 45 consecutive cases of MPN (15 ET, 15 PV, 15 PMF), 15 MDS and 15 normal bone marrow biopsies for lymphoma staging. The slides were scanned for primary diagnosis, and the size of 20 megakaryocytes was measured in a 2 mm2 area. Additionally, the number of megakaryocytes and the number and size of aggregates were also quantified. Results: The size of megakaryocytes was 11.7-53.8 μm (average 26.4 μm) in normal bone marrow and 10.8-94 μm (average 41.1 μm) in ET, 17.2-122.4 μm (average 49.5 μm) in PV, 14-92.4 μm (average 44.4 μm) in PMF and 11-53 μm (average 25.1 μm) in MDS. The differ- ences between normal, MPN and MDS were statistically significant (p<0.001). The number of megakaryocytes was not different within MPN, but the number of aggregates was higher in PV (p=0.009) and higher in size for PMF (p=0.005). Between normal and MDS, the num- ber of megakaryocyte per area was higher in MDS (p=0.049) but there were no differences in their average sizes. Conclusion: It is well known that BRC-ABL negative MPN have larger megakaryocytes. In our study, sizes above 40 μm were found to be the best cut-off to suggest a MPN, but none for MDS. However, no differ- ences in the size between the various MPN studied were found. On the other hand, the number of megakaryocytes per area was no different between MPN and MDS, but there were statistically significant when compared to MDS and normal bone marrow. E-PS-12 | E-Posters Head and Neck Pathology E-PS-12-001 Can recurrences be predicted with the histopathological changes observed in Schnederian Papillomas? Y. Adali*, S. Ekmekci, N. Akcan, Ü. Küçük *Izmir University of Economics Faculty of Medicine, Turkey Background & objectives: Inverted, exophytic, and oncocytic sub- types of Schnederian papillomas are prone to recurrence and carry the risk of malignant transformation. In this study, it is aimed to examine the predictive value of histopathological findings for recurrence. Methods: 57 schnederian papilloma cases diagnosed in a training and research hospital between 2011-2023 January were included in the study. All slides of the cases were re-evaluated in terms of metaplasia, dysplasia, lymphoid aggregates, inflammation, and stromal features. The relationship between papilloma subtype, location, demographic characteristics, histopathological findings and recurrence was evalu- ated statistically. Results: Twenty (27.8%) of the cases were female and 37 (51.4) were male. 49 (68.1%) were inverted papillomas, 4 (5.6%) were exophytic papillomas and 4 (5.6%) were oncocytic papillomas. 11 (15.3%) cases had recurrence, 32 (44.4%) had squamous metaplasia, and 9 (12.5%) had concomitant dysplasia. Eight of the dysplasias were low grade and 1 high grade. Squamous cell carcinoma development was observed on the inverted papilloma in 1 case. Although there is no significant rela- tionship between diagnosis and recurrence, all cases with recurrence are inverted papillomas. Although not statistically significant, squamous metaplasia was noted in 8 (72.7%) of 11 cases with recurrence. No significant correlation was observed between recurrence and dysplasia. Conclusion: The most important risk factor for recurrence is inadequate surgery. Although molecular alterations that predict recurrence have been reported in sinonasal papillomas, detection of these alterations is not rou- tinely performed. It is thought that the identification of predictive fac- tors that can be easily evaluated by light microscopy will facilitate patient follow-up. Although statistical significance was not found with histopatho- logical findings and recurrence in this study, the remarkable increase in numbers indicates that significance can be detected in large case series. E-PS-12-003 Central mucoepidermoid carcinoma arising in glandular odonto- genic cyst: a rare case report F. Al Hinai*, H. Al Kindi, Z. Al Hajri, M. Al Saadi *Oman Medical Specialty Board, Oman Background & objectives: Central Mucoepidermoid Carcinoma (CMC) is a rare subtype of mucoepidermoid carcinoma, which can arise from Glandular Odontogenic Cyst (GOC). This paper reported a CMC arising in GOC, focusing on the main histological and molecular features of this tumour.