ECP 2023 Abstracts

S251 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 the cauda equina neuroendocrine tumour. We compare the expression of HOXB13 in rectal NETs with the NETs of the gastrointestinal tract. Methods: HOXB13 immunohistochemical expression was assessed in 11 NETs (2 small bowel, 3 pancreas, 2 appendix, 2 rectum-L cell sub- type and 2 rectum-EC cell subtype). The monoclonal antibody against HOXB13 (AbCam, clone EPR17371, 1:2000) was used. The intensity and proportion of positive cells of the immunohistochemical marker was estimated via the Immunoreactivity Scoring System (IRS). Results: Complete absence of HOXB13 expression was found in the NETs of the small bowel (0/2, IRS 0), of the appendix (0/2, IRS 0) and of the pancreas (0/3, IRS 0). On the contrary, strong nuclear staining for HOXB13 in a high percentage of cells was observed in all the NETs arising from rectum, irrespective of the cell subtype (80-90%, IRS 12). Conclusion: The transcription factor HOXB13 appears to have strong nuclear expression in the rectal NETs in comparison to the NETs of the rest of the gastrointestinal tract, making it a valuable marker when trying to assign an origin in NETs of unknown primary, taking into consideration that it is also expressed in the cauda equina NET (for- merly known as paraganglioma of the cauda equina). E-PS-09-025 Comparative immunohistochemical study of cMYC, cyclin D1 and Ki-67/MIB-1 expression in neoplastic and non-neoplastic thyroid tissues A. Syrnioti*, E. Forozidou, A. Poutoglidis, K. Sapalidis, T. Koletsa *Department of Pathology, School of Medicine, Aristotle University of Thessaloniki, Greece Background & objectives: To investigate the immunohistochemical expression and the diagnostic utility of cMYC, cyclin D1, and Ki-67/ MIB-1 in follicular adenomas (FAs), follicular carcinomas (FCs), poorly differentiated (PDTCs) and anaplastic thyroid carcinomas (ATCs), as well as in their corresponding adjacent, non-neoplastic tissue (NNT). Methods: Twenty-eight cases were retrieved from the archives of our Department, 13 histologically diagnosed as FAs, 11 as FCs, and 4 as PDTCs/ATCs. Tissue microarrays with cores taken from neoplastic and adjacent NNT were constructed. Immunohistochemistry with cMYC, cyc- lin D1, and Ki-67/MIB-1 antibodies was performed, and the positivity was evaluated. A statistical analysis using IBM SPSS Statistics v25 followed. Results: Nuclear cMYC positivity was observed in 4/11 FCs, and 3/4 PDTCs/ATCs, whereas cytoplasmic cMYC positivity was found in 16/24 NNTs. Globally, there were statistically significant differences between neoplasms and NNTs, with higher nuclear cMYC and cyclin D1 expres- sion observed in neoplasms (p=0.017 and p=0.001, respectively), in con- trast to cytoplasmic positivity seen solely in NNTs (p=0.001). Cyclin D1 positivity was noted in 11/13 FAs, 7/11 FCs, 2/4 PDTCs/ATCs, and only in one NNT. A statistically significant correlation was found between MIB1 and c-MYC nuclear positivity (r = 0.413, p=0.040). In addition, statistically significant differences regarding the biomarker expression between FA and FC versus PDTC/ATC (p<0.001) were noted. Conclusion: Our findings exhibit a clear difference in the immuno- histochemical expression of cMYC and cyclin D1 between differ- ent types of thyroid tumours, as well as between the neoplastic and non-neoplastic thyroid tissue. Nuclear cMYC positivity excludes the benign nature of a thyroid lesion, in contrast to cytoplasmic positivity, which supports the normal or hyperplastic nature. Although a correla- tion between MIB-1 and cMYC was observed, the diagnostic value of cMYC localization proves to be superior. E-PS-09-026 Expression of somatostatin receptors in radioiodine refractory follicular cell derived thyroid carcinomas detected with [68Ga] Ga-DOTA-TOC K. Vargas Osorio*, A. Calatayud-Cubes, E.J. Díaz-López, C. Barbarán- Corral, H. Lázare-Iglesias, U. Anido-Herranz, J.M. Cabezas-Agrícola, V. Pubul-Núñez, J.M. Cameselle-Teijeiro *Clinical University Hospital of Santiago de Compostela, Universidad de Santiago de Compostela and Galician Healthcare Service (SER- GAS), Santiago de Compostela, Spain Background & objectives: There are still limited data regarding the immunohistochemical expression and relevance of somatostatin recep- tors (SSTRs) in follicular cell-derived carcinomas. We describe the clinicopathological and immunohistochemical features of three cases whose metastases were detected using [68Ga]Ga-DOTA-TOC (syn- thetic somatostatin analogue peptide). Methods: We examined three cases: widely invasive oncocytic carci- noma (case 1), widely invasive follicular cell thyroid carcinoma (case 2), and minimally invasive oncocytic carcinoma (case 3), presented in 2 men and 1 woman of 41, 60 and 46 years old, respectively. Total thyroidectomy and immunohistochemical study for SSTRs (anti-soma- tostatin receptor-2 antibody [clone UMB1] was carried out. All patients developed metastasis. Results: Case 1 (pT3b,N0,M1[at diagnosis]) was treated with I131, sorafenib, lenvatinib and chemotherapy. Given the tumour burden, intolerance to treatment, rise in levels of serum thyroglobulin and positivity for [68Ga]Ga-DOTA-TOC, a treatment with [177Lu]Lu- DOTATATE was administered. The patient died due to the disease 131 months after diagnosis. In case 2 (pT3,N0,M1[at diagnosis]) after 2 doses of I131 (250 mCi) the levels of thyroglobulin rose (5162ng/ mL). In case 3 (pT1b, N0, M0[at diagnosis]), after 2 doses of I131 (150 mCi) the levels of thyroglobulin also rose (1635ng/mL). In both cases 2 and 3, positivity for [68Ga]GaDOTA-TOC was detected. The tumour cells in all three cases showed strong immunoreactivity for somatostatin receptor 2. Conclusion: In radioiodine refractory metastatic lesions from follicu- lar cell-derived thyroid carcinomas (including oncocytic carcinomas), SSTR expression can be detected either by using radiolabelled SSTR analogues or through immunohistochemical studies. In these cases, [177Lu]Lu- DOTA-TATE is an alternative treatment modality. Funding: Supported by grant no. PI19/01316 from Instituto de Salud Carlos III (ISCIII), State Research Agency and Ministry of Science and Innovation (Spain), co-funded by the European Union E-PS-10 | E-Posters Gynaecological Pathology E-PS-10-001 Minimal volume, non-myoinvasive uterine serous carcinoma in an endometrial polyp, with isolated pleural metastasis, at presentation in a pre-menopausal patient A. Abrari*, N. Ranawaka, K. Akhtar *The Rotherham NHS Foundation Trust, United Kingdom Background & objectives: Uterine serous carcinomas are aggressive, predilecting post-menopausal women, having bulky primary tumours with extrauterine spread at the outset. The present case illustrates that even minute, non-myo-invasive serous carcinomas are sinister, can beget distant metastases and age is no bar. Methods: Concerted pathological evaluation of the miniscule, his- tologically divergent locus in the endometrial polyp, removed for abnormal uterine bleeding, and of the metastatic carcinoma detected in the pleural thickening, biopsied after imaging, following the high risk endometrial cancer diagnosis - was performed. Morphology and immunohistochemistry panels, including oestrogen receptor, vimentin, Pax8, GATA3, WT1, p53 and p16 were evaluated in both specimens. Results: The divergent, sub-millimetric locus in the endometrial polyp was interpreted as minimal, non-myoinvasive uterine serous carcinoma. The pleural biopsy demonstrated a metastatic carcinoma, essentially a facsimile of the uterine cancer. Carcinomas from both specimens had morphology and immuno-phenotype typical of uterine serous carcinoma.