ECP 2023 Abstracts

S81 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Background & objectives: PD-L1 testing in melanoma tissue samples may be challenging, due to morphological features and technical issues. The aim of the study was to develop and validate a new immunohis- tochemistry (IHC) multiplex technique to facilitate interpretation and scoring of PD-L1. Methods: Formalin-fixed paraffin-embedded (FFPE) melanoma sam- ples (n=315) were retrospectively selected. We tested PD-L1 expres- sion in 92 primary cutaneous melanoma and 223 melanoma metastases. Sections were incubated with anti-PD-L1 (Clone E1L3N) with RED chromogen. Any intensity of membranous staining on tumour cells was considered, and samples where membrane staining was obscured by high cytoplasmic staining or melanin content were be deemed indeterminate. Results: We observed that 93/315 (29.5%) melanoma cases were char- acterized by a difficult interpretation of the PD-L1 staining. This com- plexity was mainly due to the majority of tested samples 52/315 (16.5%) falling across the cutoff (1%). Additionally, 8/315 (2.5%) cases showed wide areas of necrosis and/or fibrosis and 33/315 (10.5%) were highly pigmented, both conditions that complicate the staining’s evaluation. To overcome these challenges, we developed a highly standardized multiplex- ing protocol using the RED/DAB chromogens combination. This double staining was coupled with a previously published bleaching pretreatment technique (Ugolini; 2021), in selected highly pigmented samples. Conclusion: Our results showed that brightfield multiplex PD-L1/ SOX10 double labelling could be a useful tool in challenging melanoma specimens, which may be used to colocalize SOX10+/PD-L1+cells. This technique could help pathologists in daily practices to recognize more accurately melanoma cells positive to PD-L1 membranous stain, particularly at the host-tumour interface. Finally, this technique could be useful in training phase of development of AI power tools that in future could standardize and autonomize the PD-L1 assessments. This work was funded by the Fondazione AIRC “Programma di ricerca 5 per Mille 2018—ID#21073” PS-09 | Poster Session Endocrine Pathology PS-09-001 Thyroid papillary carcinoma and multifocality Y. Adali*, S. Ekmekci, M. Üstün, Ü. Küçük, E.E. Pala *Izmir University of Economics Faculty of Medicine, Turkey Background & objectives: Papillary thyroid cancer (PTC) is the most common endocrine malignancy with an increasing incidence. Multifocality is frequently detected in PTC, but its prognostic sig- nificance is controversial. In this study, it was aimed to determine the relationship between multifocality and histopathological prognostic parameters. Methods: In the study, 513 PTC cases between the years 2012-2022 were examined. Sections of the cases were re-evaluated by 2 patholo- gists. In addition to age and gender, multifocality was compared with parameters which are known to show histopathological and prognostic importance like lymphovascular invasion (LVI), blood vessel invasion (BVI), perineural invasion (PNI), and lymph node metastasis (LN). Results: The mean age of the cases was 46.86+13.17, and 394 (76.8%) cases were female and 119 (23.2%) were male. Multifocal tumour was observed in 237(46.0%) cases. Of the multifocal cases, 128(25%) had 2 foci, 57(11.1%) had 3 foci, 29(7.7%) had 4 foci, 23(4.5%) contains 5 foci or more. No statistically significant correlation was found between multifocality and gender (p=0.372), LVI (p=0.461), BVI (p=0.191), PNI (p=0.523) and LN (p=0.156).However, in cases with multifocality, PTC was observed statistically significantly higher than microcarci- noma (PTMC) when compared with unifocal’s (p=0.000).Although fol- licular carcinoma (FC) is the most common subgroup in both groups; FC was found to be statistically significantly higher in unifocal tumours compared to multifocal tumours (p=0.000). Conclusion: Different potential prognostic factors such as patient age, tumour grade, regional and distant metastasis have been demon- strated in PT. Multifocality has been reported to be associated with increased vascular invasion, LN, advanced stage, increased risk of recurrence, and the need for more extensive treatment. In the current study, although these relationships could not be demonstrated, it was noted that multifocality was observed with PTC rather than PTMC. It seems that the controversial effect of multifocality in the management of these tumours will continue. PS-09-002 Three new gene fusions in radio-iodine refractory differentiated thyroid cancer Z. Alsugair*, F. Descotes, J. Lopez, M. Decaussin-Petrucci *Department of Pathology, Institut of Pathologie Multisite, Groupe- ment Hospitalier Sud, Hospices Civils de Lyon, Pierre-Bénite, France Background & objectives: Radio-iodine refractory differentiated thy- roid cancer is challenging to treat, with need for effective diagnostic and therapeutic strategies. Extensive molecular testing became essen- tial for identifying genetic alterations, discovering new therapeutic targets, we report three metastatic refractory thyroid cancers with new gene fusions never described before in thyroid. Methods: We performed pan-cancer DNA- and RNA-sequencing on tumour samples from 85 patients with Radio-iodine refractory differen- tiated thyroid cancer. We used bioinformatics tools to identify genetic alterations, including gene fusions, single nucleotide variants, and copy number alterations. The histological slides were reviewed to reclassify all the cases according to the 2022 WHO classification of thyroid neoplasms. Results: Among the 85 cases, we identified 13 fusions (15%) includ- ing three new gene fusions never described in the thyroid gland: UGGT1::TERT, BTBD9::TERT, and TG::IGF1R. These fusions were all associated with high-grade DTCs. The first case, a tall cell subtype of papillary thyroid carcinoma (PTC), presented a UGGT1::TERT fusion associated with a BRAF V600E mutation. In the second case, a high- grade follicular subtype of PTC, we identified a BTBD9::TERT fusion associated with a biallelic inactivation of the ATM gene and a NRAS Q61R mutation. The third case, an angioinvasive oncocytic carcinoma, harboured a TG::IGF1R fusion and was associated with a TERT promoter mutation. Conclusion: Our study highlights three novel fusions UGGT1::TERT, BTBD9::TERT and TG::IGF1R in RAI-R-DTC . These newly detected alterations extend the molecular spectrum of thyroid carcinomas and provide a novel insight into their oncogenesis and prognosis. Further investigations are needed to confirm if these fusions represent a unique subtype entity or a genotype-phenotype correlation. PS-09-003 Immature PIT1-lineage pituitary neuroendocrine tumour/ adenoma E. Athanasiou*, G. Kyriakopoulos, A. Therapontos, F. Dolkiras, P. Vlachou, I. Galonakis, M. Chrisoulaki, E. Spiteri, N. Stavrinou *Department of Pathology, Evaggelismos General Hospital Athens, Greece Background & objectives: Immature PIT1-lineage pituitary neuroen- docrine tumour/adenoma corresponds to a recently identified entity with distinctive immunohistological features, characterized by more aggressive biological behaviour. Methods: Three female patients aged 33, 44 and 53 years with mac- roadenomas in the Sella Turcica underwent transsphenoidal resection of the tumours. Results: The histological characteristics consisted of a neuroendocrine cell tumour with a bold eosinophilic nucleus with pseudo-inclusions, multilobulated nuclei with an abnormal nuclear membrane and a