ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 leading to possible misdiagnosis. Careful interpretation of MMR proteins, notably for PMS2 in absence of positive internal controls, was paramount for the accurate assessment. A correct diagnosis is of utmost importance, given the high CMMRD mortality rate, and the necessity of genetic counselling. E-PS-06-068 Gastrointestinal "juvenile-like (inflammatory/hyperplastic) mucosal polyps" as specific gastrointestinal manifestation of neurofibromatosis type 1 (NF1) – a case report D. Enea*, X. Dray, E. Guillerm, A. Guilloux, M. Yver, P. Cervera, M. Svrcek *Sorbonne Université, AP-HP, Saint-Antoine Hospital, Department of Pathology, Paris, France Background & objectives: Neurofibromatosis type 1 (NF1) is a com- mon syndrome that exhibits variable phenotypic expression. Gastro- intestinal juvenile-like (inflammatory/hyperplastic) mucosal polyps (JLIHMPs) have been proposed as a NF1-specific gastrointestinal (GI) manifestation and only a few cases were reported so far. Methods: We report a case of a 78-year-old female featuring JLI- HMPs in clinically/genetically proven NF1. A thoroughly exam- ination was carried out due to an iron-deficiency anaemia. The colonoscopy revealed two pediculated polyps located in the right colon (15mm and 23mm, respectively) and one in the left colon (60mm). Following polypectomies, microscopic examination and genetic analysis were conducted. Results: Histologically, the two right-sided polyps showed juve- nile-like features such as superficial ulceration and granulation tissue, dilated/distorted crypts separated by abundant, markedly inflamed stroma, rich in eosinophils and mast cells. Vascular changes (i.e. wall thickening) were present in the polyps axes. Additionally, squamous metaplasia was noted. The left-sided polyp exhibited similar characteristics; however, unlike the other two pol- yps, it presented foci of low-grade dysplasia. On IHC, performed on one of the right-sided polyps, CD117 staining showed numerous mast cells, stromal cells were CD34− and S100 staining did not show Schwann cells/neural alterations. Moreover, DNA analysis did not reveal any PDFRA or any specific mutations. The polyps characteristics were consistent with JLIHMPs. Conclusion: Considering the poor characterisation of this entity, the diagnosis is non-trivial. Although usually not prominent, both juvenile and fibroid polyps (IFPs) features may be found in JLIHMPs. The lack of specific mutations sustained our diagnosis. As mast cells are deregulated in NF1, a heavy inflammation with numerous mast cells suggests a possible pathogenetic role of these leukocytes. Our findings add to the current knowledge on this particular entity as it may be recognised as specific gastrointestinal manifestations of NF-1. E-PS-06-069 Mismatch repair protein status in gastric cancer: implications for diagnosis, prognosis and management L. Mascarenhas-Lemos*, J. Ricardo Silva, D. Sousa Marques, I. Gullo, X. Wen, C. Nascimento, A. Costa, A. Faria, C. Gouveia, L. Pinho, P. Patrícia, C. Fátima, M. Cravo *Department of Pathology Hospital da Luz Lisboa, Faculty of Medicine Universidade Católica Portuguesa, Nova Medical School, Portugal Background & objectives: Discordant results were reported about the benefit of neoadjuvant chemotherapy (NChT) for patients harboring gastric cancer (GC) with mismatch repair protein (MMR) deficiency. Aim: to evaluate if MMR-status is related to survival and/or response to NChT in GC patients. Methods: 116 operated GC patients with (n=46) or without (n=70) NChT were retrospectively selected from two institutions (2004-2015). Clinicopathological features were analysed. Tumour morphology was assessed according to WHO and Laurén clas- sifications. Tumours were classified as MMR-proficient (MMRp) or deficient (MMRd) by immunohistochemistry. IBM-SPSS was used for statistical analysis. For survival analysis (Kaplan-Meier). Stage IV GC patients were excluded. Results: 73/116 cases (62.9%) were MMRp and 43/116 (37.1%) were MMRd. MMRp-status was associated with poorly-cohesive (WHO) / diffuse (Laurén) histopathological subtype (n=26/73, 35.6%), while MMRd-status was associated with high-grade tubular (solid) mor- phology (WHO) (n=12/43, 27.9%) and indeterminate Laurén subtype (n=24/43, 55.8%) - p=0.003 (WHO) and p<0.001 (Laurén). Overall survival (OS) was not related to MMR status (p=0.735). There was no difference in OS in patients treated with surgery alone or NChT, as assessed in the whole series (p=0.161) and separately in MMRp (p=0.381) and MMRd (p=0.251) subgroups. Conclusion: Histopathological assessment may be important in the identification of MMR-status in GC. Particularly, in this series, high-grade tubular (solid) morphology, according to the WHO clas- sification (Laurén: indeterminate; Japanese Gastric Cancer Asso- ciation: por1), identified 27.9% of MMRd cases. In line with some studies, MMR-status was not related to OS, either in patients sub- mitted to direct surgery or NChT. These results are relevant, since over 60% of Western GC patients are diagnosed at an advanced stage and would perform NChT. Funding: Institutional grant from Luz Saúde E-PS-06-070 A case of clear cell sarcoma of the jejunum J. Gama*, R. Oliveira, A.C. Lai, J. Madeira, C. Courelas, A. Alves, G. Fontinha, F. Ramalhosa, V. Almeida, C. Faria, M.A. Cipriano *Centro Hospitalar e Universitário, Portugal Background & objectives: Gastrointestinal clear cell sarcoma is a rare neoplasm, with neuroectodermal differentiation and associated to gene fusion translocation involving EWSR1. It has a poor outcome and often it has metastasis at presentation. Methods: A 53-year-old woman presented to the emergency department with complaints of weight loss, anorexia and fatigue for the last three months. In the CT scan there was a suspicion of a jejunal mass, which was confirmed by enteroscopy. Jejunal resec- tion was performed. During the surgery, the presence of peritoneal carcinomatosis was noted. Results: On gross examination, the tumour had 4x3.5x3.5cm, with mural growth and lumen obliteration, with focal mucosa ulceration. On cut section, it was tanned, solid and lobulated. Histologically, it had a multinodular growth pattern and it was a predominantly solid neoplasm with focal areas of alveolar, glandular and papillary patterns, composed of uniform and clear cells. Immunohistochemically the cells were immunoreactive for SOX10, synaptophysin and S100, and negative for panCK, p53, Cromogra- nin, DOG1, MelanA, HMB45, PAX8 and MITF. Gene fusion involving EWSR1 was confirmed by FISH, thus giving the final diagnosis of a gastrointestinal clear cell sarcoma/malignant gastro- intestinal neuroectodermal tumour No recurrence or progression was reported after 5-months. Conclusion: Gastrointestinal clear cell sarcoma/malignant gastrointestinal neuroectodermal tumour is a rare neoplasm. Although uncommon, it should be considered on the differential diagnosis for melanoma metastasis in the bowel, because of S235