ECP 2023 Abstracts

S213 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 subserosa and serosa in some areas, with lymphovascular and perineu- ral invasion. There was ectopic mucosa of gastric type with foveolar epithelium. Immunohistochemically, the tumour presented epithelial cell differentiation and was negative for neuroendocrine markers. There was heterogenous loss of membranous immunopositivity of E-cadherin in the poorly cohesive areas. Two-months later, the patient presented with intestinal obstruction again and was submitted to exploratory lapa- rotomy that revealed ascites and peritoneal carcinomatosis, compatible with peritoneal involvement. Conclusion: MD may be asymptomatic and diagnosed incidentally or associated with complications, like intestinal obstruction. Primary malignancies of the MD are unusual. Although adenocarcinomas are exceedingly rare, they have a very poor prognosis, due to the advanced stage associated with late detection. It has been suggested an association with heterotopic tissue located within the diverticulum, like gastric mucosa, however the cause is unknown. There is no con- sensus on the best treatment and staging for adenocarcinomas in MD. E-PS-06-080 In silico analysis of serrated adenocarcinoma morphology in colo- rectal carcinomas Z. Sağnak Yılmaz*, M.H. Toper, S. Sarioglu *Dokuz Eylül University, The Institute of Health Sciences, Department of Molecular Pathology, Karadeniz Technical University, Faculty of Medicine, Department of Pathology, Turkey Background & objectives: Serrated adenocarcinoma (SAC) is a sub- type of colorectal carcinoma (CRC) differentiated by serration, eosino- philic cytoplasm, vesicular nucleus, mucinous or trabecular pattern. In this pioneering study, molecular changes in the development of SAC were investigated in silico for the first time. Methods: Data from cBioPortal for Cancer Genomics (cBioPortal) and The Cancer Genome Atlas (TCGA) were used. 181 of TCGA CRC microscopic images were examined. The cases were classified as classical adenocarcinoma and SAC. Stage, prognosis, mutation, meth- ylation, and mRNA expression data were obtained from cBioPortal using case numbers, and the two groups were compared for each data. Results: Classical adenocarcinomas (148 cases, 81.8%) and SACs (33 cases, 18.2%) were compared. BRAF, PIK3CA, EGFR, ERBB2, RET, MET mutations were found at a higher rate in SACs, while KRAS, NRAS, APC, TP53 mutations were found at a higher rate in the classical type, but a significant p value was obtained only for TP53 (p=0.019). ZNF714 DNA methylation rate were higher in the classical variant, FLOT1, SLX1B, MLLT11, PENK DNA methyla- tion rates were higher in SACs and a significant difference was found (ZNF714 q<0.000, FLOT1 q=0.0173, SLX1B q=0.0173, MLLT11 q=0.0173, PENK q=0.0414, all p<0.000). Mean life expectancy is 56.21 months in patients with SAC and 61.79 months without SAC (p=0.121). Conclusion: In this pioneering study, significant p and q values for ZNF714, FLOT1, SLX1B, MLLT11, PENK DNA methylation were determined when SACs and classical adenocarcinomas were compared. There is no comprehensive study on DNA methylation in SACs in the literature; this result is unique. A significant p value was found for the TP53 mutation, but no significant q value was found. E-PS-06-081 RAS status by Idylla technology-what’s about the invalid cases? G. Sahraoui*, H. Douik, L. Charfi, R. Doghri, I. Nasri, D. Ghezala, K. Mrad *Salah Azaiez Institute, Tunisia Background & objectives: Idylla technology is an automated real time-PCR system allowing rapid molecular analysis of RAS/BRAF mutations in metastatic colorectal cancer. We evaluated the rate of “invalid cases” in a series of colorectal patients screened for KRAS mutations by the Idylla system. Methods: 830 patients with metastatic colorectal cancer were enrolled. Sections of formalin-fixed paraffin-embedded tumour tissue were put on a Idylla Test cartridge. Results of codons 12, 13, 59, 61, 117, and 146 mutation screening are revealed directly on the console. If no muta- tion was found in the KRAS gene, a screening for NRAS and codon 600 BRAF gene mutations were performed. Results: KRAS/NRAS-BRAF mutations screening showed a total of 50 invalid cases (6%) between KRAS and NRAS-BRAF testing. For the Kras test, 14 cases were screened twice: 10 among them remained invalid, 3 became “non-mutated” and one kept a G12C mutation after a second screening. For the NRAS-BRAF test, 4 samples were tested twice; all remained “Invalid”. Patients’ histopathological characteristics don’t show any correlation with invalid cases, but we noted that 35 invalid cases were rich in tumour cells (≥30%), and only 15 had unless of 20%of tumour cells; therefore,29 were the result of surgical samples and 20 were issues from biopsies. Conclusion: Invalid cases should not be overlooked in the Idylla RAS- BRAF mutation test. Our study highlights the importance of the quality of the surgical sample or biopsy’s fixing for a good quality of DNA, essential as a support for molecular diagnosis. E-PS-06-082 A gastric follicular dendritic cell sarcoma: report of a rare inci- dental diagnosis G. Sahraoui*, F. Sassi, I. Zemni, S. Chaabouni, H. Guizani, L. Charfi, R. Doghri, K. Mrad *Salah Azaiez Institute, Tunisia Background & objectives: Follicular dendritic cell sarcomas (FDCS) are rare tumours, typically seen in lymph nodes. The extranodal involvement is rarer. The aim of this study is to review clinicopatho- logical features and emphasize on differential diagnosis and therapeutic modalities of this rare entity. Methods: We report on a 36-year-old female patient with no past medi- cal history. The patient was brought in for management of an axillary furuncle. Upon further examination, she mentioned experiencing mild difficulty in breathing but did not report any abdominal pain. Apart from having a moderate level of anaemia, her physical examination and laboratory testing did not reveal any significant findings. Results: Abdominal ultrasonography was performed, revealing a 4 cm well-defined gastric mass. Athoraco-abdomino-pelvic CT scan was per- formed, showing an increase in tumour size to 9 cm with the presence of deep and retro-pancreatic lymph nodes. The mass was biopsied for histological examination. It showed a tumour composed of large, oval to spindle-shaped cells organized in sheets and interlacing fascicles. Numerous small lymphocytes coexisted with the tumour cells. Immu- nohistochemically, tumour cells expressed CD21 and CD23. They were negative for AE1/AE3, CD34, c-kit, DOG-1, CD20, CD30, CD10, bcl-6, CD68, S-100, D2-40, CD45, or EBER. The diagnosis of FDCS was retained. The tumour was resected by gastrectomy with extended para-aortic lymphadenectomy, with uneventful postoperative course. Conclusion: Morphological pattern of FDCS may overlap with a broad range of potential differential diagnoses. A distinction from better known mesenchymal sarcomas, such as the gastro-intestinal stromal tumours, inflammatory myofibroblastic tumours Eptein-Barr Virus positive or interdigitating dendritic cell sarcoma must be considered. Complete surgical resection is the current gold standard of treatment. E-PS-06-083 Incidental histopathological findings in sleeve gastrectomy speci- mens for weight management E. Salmo*, A. Cotterill *Royal Oldham Hospital, United Kingdom