ECP 2023 Abstracts

S250 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 tumours causing severe hypercalcemia and hypophosphatemia, and patients often present both renal and bone disease. Most parathyroid carcinomas are sporadic, but a genetic test is recommended due its association with hyperparathyroidism-jaw tumour syndrome (HRPT2/ CDC73 gene), familial isolated hyperparathyroidism (HRPT2 gene and others) and multiple endocrine neoplasia type 1 and 2A syndromes (MEN1 and MEN2A genes). E-PS-09-021 Morular cribiform thyroid carcinoma: two-case series A. Sifre-Ruiz*, A. Onaindia-Pérez, È. Iglesias Martínez, N. Santi- ago-Quispe, M.M. Buda, C. Esquina, A.M. Cordovilla-Moreno, B. Catón-Santaren *Clinical Department Unit of Pathological Anatomy, OSI Araba, Araba University Hospital. Bioaraba Health Research Institute, Vitoria- Gasteiz, Alava, Spain., Spain Background & objectives: We report two cases of morular cribriform carcinoma (MCC): a twelve-year-old female (patient 1) with previous diagnosis of familial adenomatous polyposis syndrome (FAP) and a twenty-year-old one without any antecedents (patient 2). Both pre- sented goiter with Bethesda V category nodules. Methods: Thyroidectomy specimens were studied, including hema- toxylin-eosin stains; additional inmunohistochemical stains (Ventana BenchMark ULTRA, Ventana Medical Systems, Inc., Tucson, AZ, US) and complete APC sequencing (Sanger sequencing method using MLPA technique in an ABI3130x analyzer). Clinical data, personal and family history of the patients were investigated. A descriptive analysis of the obtained data and a literature review were carried out. Results: Macroscopically both specimens showed well-demarcated, bilateral solid nodules, corresponding microscopically to epithelial proliferations surrounded by a thick fibrous capsule, exhibiting diverse growth patterns, predominantly cribriform. Empty spaces with a striking absence of colloid were lined up by cuboidal or columnar tumour cells, with eosinophilic cytoplasm and elongated and irregular nuclei with a tendency to “crowding”. Non-keratinizing squamoid morulae were also present in all sections. Immunohistochemical studies showed negativity for thyroglobulin; TTF-1 and β-catenin nuclear and cytoplasmic positiv- ity was identified. A diagnosis of MCC was made in both cases. APC sanger sequencing was performed in patient 2 specimen, revealing a probably pathogenic variant [c.3548del, p.(Tyr1183Leufs*82)]. Conclusion: MCC is often associated with FAP (in up to 40% of the cases, precedes its diagnosis), presenting at young age with goiter. MCC has been recently catalogued as a separate entity in the 5th WHO classification of tumours of endocrine organs. Germinal or somatic mutations, conditioning biallelic APC gene inac- tivation, trigger WNT/β-catenin pathway constitutive activation, which is essential for MCC pathogenesis. This tumour’s peculiar morphology and characteristic immunohistochemical features, allow a prompt diag- nosis enabling molecular testing for FAP syndrome screening. E-PS-09-022 Indicators of epithelial-mesenchymal transformation in patients with papillary carcinoma of the thyroid gland and its combination with chronic autoimmune thyroiditis I. Sorokina*, N. Filonenko, O. Kaluzhyna *Kharkiv National Medical University, Ukraine Background & objectives: Papillary thyroid carcinoma (PTC) is the most common form of thyroid cancer. The aim of the work is to establish the features of epithelial-mesenchy- mal transformation (EMT) in patients with PTC and its combination with AIT through a complex pathomorphological study. Methods: Histological, immunohistochemical, morphometric, and statistical methods were used in the work. The material is divided into three groups: PTC (25 cases), AIT (10 cases) and PTC on the back- ground of chronic AIT (25 cases). We investigated pancytokeratin and keratin-7, vimentin, and E-cadherin. The percentage of cells expressing the marker in the field of view was determined, ×400. Results: In the immunohistochemical study of thyroid tissue with PTC, it was established that pancytokeratin and keratin-7, as well as E-cadherin are expressed by the follicular epithelium of tumour struc- tures weakly ("+"), while the expression of vimentin is evaluated as expressive ("+++"). This indicates the presence of EMT. Combina- tion of PTC with AIT is characterized by moderate expression ("++") of all investigated markers, which indicates a relative decrease in the manifestations of EMT in this group compared to PTC. Conclusion: In the group of PTC, there is a decrease in the expression of E-cadherin, as well as a decrease in the expression of pancytokeratin and keratin-7 with a pronounced expression of vimentin. The described changes are characteristic of EMT phenomena. Thus, it can be assumed that the presence of AIT in a patient with PTC is a prognostically favourable circumstance for the course of the tumour process. E-PS-09-023 Immunohistochemical detection of Sine oculis homeobox 6 (SIX6) in clinically silent pituitary neuroendocrine tumours – a pilot study J. Soukup*, H. Faistova, L. Gerykova, P. Poczos, T. Česák, M. Kosak, D. Netuka, F. Gabalec *University Hospital Hradec Kralove, Czech Republic Background & objectives: Sine oculis homeobox 6 (SIX6) is a tran- scriptional factor expressed in pituitary gland, playing role in differen- tiation of gonadotroph lineage. There are however no data about SIX6 in PitNETs or other sinonasal neoplasms. Methods: Immunoreactivity of SIX6 (polyclonal, Atlas Antibodies, 1:50) was examined in 20 non-functional PitNETs (10 gonadotroph, 5 corticotroph, and 5 Pit1-lineage) using immunoreactivity score (IRS). Normal pituitary was used as a positive on slide control. Additional data on mitotic activity, Ki67, p53 and tumour recurrence were analysed. Results: SIX6 expression in normal pituitary tissue was heterogene- ous, with strongly, weakly positive and negative cells. SIX6 immuno- reactivity was detected in 18/20 (90%) PitNETs; two negative cases corresponded to Crook cell tumour and poorly differentiated Pit1+ tumour. IRS ranged from 1 to 8, with median IRS 3, and no difference was observed among the three lineages (p=0.69; Kruskal-Wallis test). Compared to strongly positive cells in normal pituitary, only moderate (6/18; 33.3%) or weak (12/18; 66.6%) immunoreactivity was observed in tumour tissue. We observed no difference in IRS among recurrent and non-recurrent tumours (p=0.78; Mann-Whitney test) and no cor- relation between SIX6 and Ki67 or mitotic activity. Conclusion: Although SIX6 can be detected in non-functional Pit- NETs across all lineages, its immunoreactivity is usually weak and limited compared to normal pituitary tissue. This limits its use as a general marker of pituitary tumours in differential diagnosis of head and neck neoplasms. Funding: Ministry of Health, Czech Republic, NU20-03-00360; BBMRI-CZ LM2023033; Czech Ministry of Defense MO 1012 E-PS-09-024 Expression of the transcription factor HOXB13 in the neuroendo- crine tumours of the gastrointestinal tract E. Spiteri*, N. Stavrinou, F. Dolkiras, P. Vlachou, E. Athanasiou, A. Therapontos, M. Tsoli, M. Panagaki, G. Kyriakopoulos *Department of Pathology, Evaggelismos General Hospital Athens, Greece Background & objectives: The HOXB13 gene encodes a transcription factor expressed in the embryonal tail bud. HOXB13 is expressed in