ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 E-PS-06-023 The effect of counting mitosis by phosphohistone-3 immunoh i s t o ch emi s t r y on r i s k c a t e g o r i z a t i on i n gastrointestinal stromal tumours G. Bülbül*, Ö. Sağol, M. Ünlü, S. Sarıoğlu *Dokuz Eylül University Hospital, Turkey Background & objectives: The number of mitoses is among the criteria for risk categorization in gastrointestinal stromal tumours (GISTs). In this series, mitotic count by phosphohistone-3 (PHH3), a mitotic biomarker, is compared with hematoxylin&eosin (H&E) mitotic counting to understand risk category migration. Methods: In a series of 38 GIST patients, mitosis was counted with 3 methods, in 5 mm2 area: 1) All the mitotic figures in H&E stain (H&EM), 2) Only PHH3 positive cells with mitotic morphology (PHH3+MM), 3) All PHH3 positive cells (PHH3+). The risk group of each case was determined with each method and stage migration with PHH3 methods was evaluated. Results: The number of mitoses was lower in 4 (10.50%) cases, equal in 8 (21%) cases, and higher in 26 (68.50%) cases in PHH3+MM compared with H&EM method. In the PHH3+MM method, the risk category was increased in 5 (13%) patients, compared with H&EM. In the PHH3+ method, including tumour nuclei probably at pro- phase, rates were higher than the first method. The number of mitoses was equal in 5 (13%) and higher in 33 (87%) cases; 16 (42%) patients were reclassified in a higher risk category com- pared with H&EM. None of our patients migrated to a lower risk category group in both methods. Conclusion: Our results emphasize that when the method is changed, there is a migration to a higher risk category in GISTs. Therefore, H&EM should be the gold standard till the morpho- logic criteria of alternative methods like PHH3 counting is strictly described and risk categorization according to such methods is specified in large series with prognostic information. E-PS-06-024 Primary retroperitoneal mucinous neoplasia with borderline malignancy / with low malignant potential H. Geddert*, T. Rüdiger, J. Baral *Institute of Pathology, Municipal Hospital of Karlsruhe, Germany Background & objectives: An 83-year-old female patient complained of leg swelling present for several weeks. MRI imaging showed a left-sided, very large multiloculated cystic lesion, extending from the renal lodge to the inguinal canal. Methods: Thin-walled cysts without internal structure were ini- tially interpreted as lymphangioma. An area of contrast-enhancing intraluminal proliferations in the mid-abdomen was considered a secondary malignancy. Intraoperatively, a 29 x 20 x 7 cm mass fused to the descending colon was found. Complete surgical removal without cyst rupture was achieved. Results: Macroscopically, several cysts filled with viscous mucus were noted. Microscopically, the fibrous wall was lined by mucinous epithelium without cytological atypia. The suspicious finding on imaging corresponded to a thick-walled cyst with complex papillae, low-grade atypia and a markedly increased proliferation index with Ki-67. Immunohistochemistry confirmed intestinal differentiation with positivity for CDX-2, CK20, CEA, mucin2, mucin 5AC, and ß-catenin. Microscopically, there was also focal epithelial rupture with associated histiocytic demarcation and calcifications as well as fibrous adherence to the colonic wall. An infiltrative growth pattern was not found. Conclusion: We diagnose the very rare entity of a primary retroperitoneal mucinous tumour of borderline malignancy/ with low malignant potential. Metaplastic emergence from scattered multipotent mesothelial cells is a widely accepted theory regarding the histogenesis of these lesions. Currently, the patient remains well at follow up of six months without any additional therapy. A favourable prognosis can be assumed with complete surgical removal. E-PS-06-025 A rare case of colon adenosquamous carcinoma E. Souka*, G. Galanopoulos, N. Novkovic, L. Karelis, P. Manikis, G. Stanc *Pathology Department Metaxa Cancer Hospital, Greece Background & objectives: Colon adenocarcinoma (AC) is the third commonest carcinoma worldwide, but primary colon adenosquamous carcinoma (ASC) is an unusual variant accounting for < 0,1% of the tumours. We present a rare case of colon adenocarcinoma and brief review of the literature. Methods: A 53-year-old male with hematochezia underwent colonoscopy with endoscopic polypectomy and ink spotting for an ascending colon polyp. Microscopic examination revealed an ade- noma with high grade dysplasia. Subsequently a right colectomy was performed. On gross sectioning, we observed a haemorrhagic inked area of the mucosal surface measuring 3cm and thorough sampling was performed. Results: Microscopical examination revealed residual adenomatous elements of the mucosa with low grade epithelial dysplasia and an underlying submucosal carcinoma, low grade. It consisted of a well differentiated glandular carcinomatous component with a CK7(-), CK20(+), CDX2(+) immunophenotype and a well differentiated squamous cell carcinomatous component with a p63(+), p40(+), CK5/6(+) immunophenotype. The morphological and immunohistochemical findings were consistent with an ascending colon adenosquamous carcinoma. Conclusion: Colon ASC is more commonly located at the right colon. There are four hypotheses on the ASC histogenesis that include ectopic squamous cells, transformation of uncommitted basal cells, squamous metaplasia of glandular epithelium and squamous metaplasia of adenocarcinoma cells. ASC has worse prognosis than AC, since 5-year survival rates of ASC and AC are approximately 30% and 50–60%, respectively and complete surgi- cal excision is mandatory. E-PS-06-026 Glomus coccygeum: a case report of an incidental finding C.M. Vieru*, Y. Gómez Navarro, M. Garcia Martos *Hospital General Universitario Gregorio Marañón, Spain Background & objectives: Glomus coccygeum is a phylogenetic vestigial anatomical structure consisting of an arteriovenous anasto- mosis surrounded by glomus cells, involved in thermoregulation. It is incidentally found in sacrococcygeal resection specimens resected in patients with coccygodinia or advanced rectal and uterine carcinomas. Methods: We describe a case of glomus coccygeum incidentally identified in the recurrence sacrococcygeal resection specimen of a 52 years-old man diagnosed with colorectal adenocarcinoma with mucinous differentiation. Results: Macroscopically, it was a well-defined whitish nodular lesion with cartilaginous consistency, measuring 0,6x0,5 cm. His- tologic examination revealed a well-circumscribed appearance with densely packed clusters and nests of glomic cells, intimately associ- ated with vascular channels and nerve fibres, embedded in fibrous connective tissue. The cells were epithelioid, with eosinophilic S223