ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 Methods: A 44-year-old male presented with a 10-month history of weight loss, epigastric pain, inability to eat and vomiting. In endoscopic examination, an ulcerated mass lesion of 7-8 cm in diameter in the antrum was detected. The endoscopic biopsy was reported as adenocarcinoma and total gastrectomy was performed. Results: In the gastrectomy specimen, an ulcerated tumour (Bor- rmann Type III) measuring 8x6.5x1.7 cm was observed in the antrum on the lesser curvature. Histologically, the tumour was composed of differentiated areas with glandular structures and poorly differentiated areas consisting of individually infiltrating malignant cells. The cells in both components have abundant cyto- plasm containing eosinophilic coarse granules and centrally located nuclei. The cytoplasm of tumour cells was strongly immunoreac- tive for lysozyme and showed dPAS positivity. The findings were compatible with Paneth cell carcinoma. The tumour was staged as pT4aN3a with metastasis in 11 lymph nodes. The patient did not receive adjuvant treatment and has been living disease-free for 10 months. Conclusion: Although rare, Paneth cell carcinoma has unique histopathological features. One should be aware of this rare gas- trointestinal adenocarcinoma subtype to diagnose. Because of its rarity, its pathogenesis and prognostic features are still needed to be established by larger series. E-PS-06-049 A rare case of synchronous gastrointestinal stromal tumour and primary peritoneal mesothelioma - coincidental or not? E. Ignat*, A. Cioroianu, L. Sticlaru, M. Cioplea, D. Raduta, M. Filip, S. Zurac *Colentina Clinical Hospital, Romania Background & objectives: Gastrointestinal stromal tumour (GIST) represents the most common mesenchymal neoplasm of the digestive system and is frequently diagnosed with other types of primary malig- nancies. Nonetheless, primary peritoneal mesothelioma (PPM) occurs rarely even individually, thus a synchronism with GIST is exceptional. Methods: We present the case of a 78-year-old female patient with- out relevant medical or occupational history, who presented to our clinic with complaints of diffuse abdominal pain and weight loss. After careful clinical and imagistic examination, the suspicion of GIST with diffuse peritoneal metastasis was raised. Patient under- went surgery where the gastric growth and a fragment of peritoneal tumour were excised. Results: By means of histopatologic and immunohistochemistry analysis, we confirmed the diagnosis of gastric GIST that developed strong positivity for CD34, c-kit and DOG1 and was classified within the second prognostic group (with a 1.9% chance of progressive disease). The peritoneal growth surprised us from the beginning, as it did not share any morphological features with the gastric counterpart. The histology revealed a proliferation composed of epithelioid and spindle cells suggesting a carcinoma with sarcomatoid differentiation. The tumour tested positive for calretinin, WT1, caldesmon, CK 5/6, CK 7 and podoplanin, which was consistent with the diagnosis of biphasic peritoneal mesothelioma. Conclusion: Primary peritoneal mesothelioma, although infrequent, is a diagnosis that must be acknowledged, because it has a different therapeutic management as compared to peritoneal metastasis. There are very few cases in literature that report similar associations between GIST and mesothelioma, one of them actually suggesting VEGF as a possible factor linking these divergent malignancies. Standardized research on other molecular interactions between co-existing tumours could change our whole approach on this matter. E-PS-06-051 Histopathological evaluation of gastrointestinal stromal tumours Z. Bayramoglu, S. Yilmaz Erozbek*, E. Kuzucular, F. Özden *Istanbul Medipol University, Pathology Department, Turkey Background & objectives: Gastrointestinal stromal tumours (GIST) are rare tumours that account for less than 0.2% of all gastrointestinal system tumours. We aimed to investigate the histopathological and clinicopathological features and survival of GIST cases in our archive of the last 6 years. Methods: Demographic, histopathological and clinicopathological data of cases diagnosed with primary GIST in Istanbul Medipol University Faculty of Medicine Department of Pathology between 2016-2022 were evaluated retrospectively. Results: Seventy eight primary GIST cases were evaluated. Forty two (53.8%) of the cases were male and 36 (46.1%) were female. The mean age at the time of diagnosis was 59 (range: 33-91). Fifty of the tumour cases (64.1%) were located in the stomach. The mean number of mitosis was 7.1 in 50 high magnification fields, 48 cases with ≤5 and 30 cases with >5 were detected. The mean Ki-67 proliferation index was 6.4%. Liver metastasis was detected in 7 of the cases with primary diagnosis, and lymph node metastasis was detected in 2 of them. Conclusion: Standardization of histopathological reporting is of great importance for risk assessment in GIST cases. E-PS-06-052 Evaluation of mismatch repair status in colorectal carcinoma S. Yilmaz Erozbek*, Z. Bayramoglu, E. Kuzucular, F. Özden *Istanbul Medipol University, Pathology Department, Turkey Background & objectives: Colorectal carcinomas are among the most common malignancies in terms of morbidity and mortality worldwide. This study aims to analyse the mismatch repair (MMR) status and histomorphological features of cases with colorectal carcinoma. Methods: Patients with a histological diagnosis of colorectal carci- noma in our hospital in the last 6 years were included in the study. Immunohistochemical techniques for the expression of MMR pro- teins (MLH-1, MSH2, MSH6, and PMS-2) were performed. MMR status and histomorphological features of the cases were analysed. Results: Nuclear expression was observed in DNA mismatch proteins in 167 (89.7%) of the cases, while nuclear expression was lost in 19 (10.2%) cases. In the mismatch deficient group, 12 cases showed nuclear loss of MLH-1 and PMS-2, 5 cases showed nuclear loss of MSH-2 and MSH-6, and 2 cases showed nuclear loss of PMS-2. It was observed that the right colon involvement was prominent, including 15 of the 19 cases in the mismatch deficient group, right colon, 3 left colons, and 1 transverse colon tumour, but cases with left colon involvement were also seen. Conclusion: It is known that mismatch deficient tumours are associated with a better prognosis. We think that the routine application of mismatch deficient immunohistochemical examination to all colorectal carcinoma cases may be important in terms of clinical guidance for cases without clinical and histomorphological features. E-PS-06-053 Morphometric parameters of esophageal mucous in young people with gastroesophageal reflux disease and autoimmune thyroiditis S230