ECP 2023 Abstracts

S226 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 independent identity, representing <1% of all pancreatic tumours, mak- ing the management of this disease challenging as literature is scarce. Methods: We present the case of a 60-year-old man who presented to the emergency service with subocclusive symptoms and abdominal pain on 06/10/22, where an abdominal CT scan revealed an pancreatic nodule immediately distal to the uncinate process measuring 2.3cm. A FNA biopsy was obtained and the patient was later accepted for surgical resec- tion and submitted to cephalic duodenopancreatectomy on 16/02/23. Results: The biopsy revealed cells with accentuated atypia and pleomor- phism and giant multinucleated osteoclast-like cells, correlating with the definitive histological exam which determined the final diagnosis as UC-OGC with a small component of ductal adenocarcinoma, with TNM staging of pT2 N0 M0. The patient has remained stable after clinical discharge and is currently being considered for adjuvant chemotherapy as of the latest follow-up consultation on 14/04/23. The presence of associated pancreatic ductal adenocarcinoma with UC- OCG has emerged as an important criterium for prognosis, presenting lower median overall survival than pure UC-OCG. Patients who undergo surgical resection and receive adjuvant chemotherapy also seem to pre- sent longer disease-free survival and overall survival. Conclusion: As evidence points to pure UC-OGC presenting less aggressive tumoral behaviour than other undifferentiated carcinomas of the pancreas, careful histological characterization of the tumour is increasingly important. The differences in tumour composition may allow for new potential thera- peutic targets, such as immunotherapy for PD-L1 positive UC-OCG. Due to the rarity of UC-OGC, the role of chemotherapy has not yet been standard- ized. As such, more thorough research will be challenging but potentially rewarding in providing further treatment options for these patients. E-PS-07-029 Hepatic progenitor cells within a GIST liver metastasis: focusing on the role of the liver metastatic niche J. Lobo*, J. Gama, R. Luís, D. Tiniakos, M.A. Cipriano *Portuguese Oncology Institute Porto, Portugal Background & objectives: Recent studies have highlighted the pres- ence of hepatic progenitor cells (HPCs) in liver metastases, specifi- cally of carcinomas. It is theorized that HPCs may influence homing of tumour cells to the liver. Methods: We provide further evidence of this phenomenon, present- ing a case of a gastrointestinal stromal tumour (GIST) liver metastasis with evidence of intra- and peritumoral HPCs. Clinical annotation and immunohistochemistry studies are provided, along with discussion of the available literature. Results: A 64-year-old man presented with a gastric mass, diagnosed as a high-risk KIT-mutated GIST. The patient was treated with Imatinib, recurring five years later with a liver mass. Liver biopsy disclosed a GIST metastasis, showing a proliferation of ductular structures without cytological atypia intermingled with the tumour cells, with a K7/K19/ CD56-positive immunophenotype and rare CD44 positivity. The patient underwent liver resection, and the same ductular structures were present in the tumour interior and at its periphery. Conclusion: The ductular structures were positive for the biliary marker K7 and the HPC markers K19 and CD56, with rare cells expressing the stem cell marker CD44, paralleling previous findings in liver metastases of colorectal adenocarcinoma. HPCs may attract cancer cells, giving rise to pre-metastatic niches, and they could have a vital role in cancer growth. E-PS-07-030 Neo-adjuvant treatment of hepatic metastases of colorectal cancer: predictive factors of histological response I. Mallek*, S. Ben Slama, Z. Ben Romdhane, B. Bouchabou, M. Mbarek, M. Hajri, H. Mestiri, A. Lahmar, D. Bacha *Monji Slim La Marsa, Tunisia Background & objectives: Surgery after neoadjuvant chemotherapy (CT) improves prognosis of colorectal cancer (CRC) with liver metas- tases (LM). Histological response is a good prognostic factor. The aim of this study was to evaluate predictive factors of histological response of LMCRC after neo-adjuvant treatment. Methods: Retrospective study of patients with LMCCR operated after neoadjuvant CT treatment from June 2016-June 2022. Assessment of histological response was based on the Rubbia-Brandt TRG tumour regression score. We grouped the scores into two types of response: Response Group (R) and No Response Group (NR). Results: We studied 77 patients. Synchronous LM was present in 55% and metachronous LM in 45%. The mean time to onset of LM was 22 months. Neoadjuvant treatment included CT alone in 68% and CT with targeted therapy in 32%. Overall survival was 32 months, with a significantly greater survival in Group R (p=0.001). Predic- tive factors for histological response included delay in onset of LM >14 months (p=0.027), neoadjuvant treatment with CT and targeted therapy (p=0.031), and absence of lymph node metastases on LM specimens (p=0.014). In multivariate analysis, neoadjuvant treatment type (p=0.035) and absence of lymph node metastases on LM speci- mens (p=0.013) were independent predictive factors of histological response. Conclusion: Predictive factors of histological response would allow to identify patients who would benefit most from neoadjuvant treatment. These are patients with LM onset of more than 14 months, treated with CT combined with targeted therapy and without lymph node metastases would be the best candidates for a neoadjuvant CT strategy followed by surgical resection. E-PS-07-031 Comprehensive characterisation of acinar cystic transformation of the pancreas: a systematic review P. Mattiolo*, H. Wang, A. Scarpa, C. Luchini *Department of Diagnostics and Public Health, Section of Pathology, University and Hospital Trust of Verona, Italy Background & objectives: Acinar cystic transformation (ACT) of the pancreas is a poorly understood pancreatic lesion. Few cases are reported, mainly as single case reports. Based on a systematic review of the literature, this study aims to comprehensively characterize this lesion. Methods: For the systematic review, two investigators (P.M.. and C.L.) independently conducted a literature search using PubMed and SCOPUS without language restriction, from database incep- tion until 03/31/2023. All data were extracted independently by two authors (P.M. and C.L.) and then validated by other authors (A.S. and H.W.). Results: The main results can be summarized as follows: 1) Total num- ber: 118 cases of ACT are reported; 2) Macroscopy: pancreatic head is the most common site (56%); ACT is more often unifocal (70%), and with multilocular structure (61%); 3) Microscopy: all cysts are lined by acinar cells without significant atypia. A not-negligible subset of cases shows ductal-like areas (18%), squamous metaplasia (8%), mucinous metaplasia (6%), and PanIN-like changes (3%); 4) Immunohistochem- istry: acinar cell markers and CK7 diffusely are positive in all cases; 5) Molecular landscape: KRAS and SMO mutations have been demon- strated in two cases; 6) Clinical course: all patients are alive and free of disease after surgical resection. Conclusion: ACT is an under-recognized entity, with specific histo- logical and immunohistochemical characteristics. Patients with ACT have excellent prognosis after surgical resection. Recognition of this rare entity is fundamental in the differential diagnosis of cystic lesions of the pancreas. The recent report of somatic pathogenic mutations of KRAS and SMO suggests the possible neoplastic nature at least in a subset of ACTs.