ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 PXA were BRAF-mutated in 6 cases, TP53-mutated in 3 and RB1- altered in none. All six cases with BRAF mutation were BRAF p.V600E positive; no PXA was RB1 negative or P53 positive. Conclusion: An immunohistochemical profile consisting in RB1 loss associated with, or alternative to, P53 positivity had the same specificity (100%), but higher sensitivity (91% vs 61%) for GC- GBM than P53 positivity alone. The addition of RB1 staining in an immunohistochemical algorithm including P53 and BRAF p.V600E may be helpful to differentiate GC-GBM from PXA. OFP-13-002 Myoepithelial neoplasia of central nervous system: a series of 4 cases S. Yeni Yildirim, K. Kosemehmetoglu*, F. Soylemezoglu *Hacettepe University, Department of Pathology, Turkey Background & objectives: Myoepithelial neoplasms, composed of myoepithelioma and myoepithelial carcinoma, have not been documented in the central nervous system. Here we present clinicopathological characteristics of 4 neoplasms with myoepithelial differentiation involving the brain and spinal cord. Methods: The clinicopathological findings of 4 cases were evaluated: 1) 16-year-old female with a 6-cm tumour in the right frontoparietal region.2) 24-year-old female with a 6-cm tumour in T12-L2. 3) 8-year-old female with a 3,5-cm tumour in T11-L1. 4) 20-year-old female with a 3-cm tumour in C4-T2. Spinal tumours were located in intradural-extramedullary space, and the cranial tumour was dural-based. Results: All patients were female with a mean age of 17(8-24). Histopathologically; 3 tumours were characterized by nests/ cords and sheets composed of malignant epithelioid/rhabdoid cells in myxocollagenous background at least focally, thus categorized as myoepithelial carcinoma. Case 2 was reminiscent of myoepithelioma/mixed tumour of soft tissue; however, showed a malignant behaviour. We found loss of INI1 expression in 3 of 4 cases; S100+EMA coexpression, and positivity for at least one keratin marker in all cases. SMA was positive in 3 of 4 cases. Break-apart FISH revealed EWSR1 rearrangements in 2 of 3 cases. Two cases (cases 2 and 3) died, one of whom (case 2) with multiple recurrences and lung metastasis. Conclusion: Myoepithelial neoplasms occur in the central nerv- ous system of children and young adult females and should be considered in the differential diagnosis of INI1 deficient tumours, after exclusion of AT/RT, poorly-differentiated chordoma, and epi- thelioid sarcoma. Multiple myoepithelial marker expression and INI1 loss along with EWSR rearrangements favour the diagnosis of myoepithelial neoplasm. OFP-13-003 Solitary fibrous tumour of central nervous system: a series of 23 cases O. Sular, B. Babaoglu, G. Yazici, K. Kosemehmetoglu*, F. Soylemezoglu *Hacettepe University, Department of Pathology, Turkey Background & objectives: Meningeal solitary fibrous tumour is characterized by fibroblastic proliferation with hemangiopericy- tomatous pattern and NAB2::STAT6 alterations. Here, we present clinicopathological features of our series with a special emphasis on the predictability of biological behaviour with the current grad- ing schemes. Methods: The clinical, radiological, and pathological findings of 23 cases were evaluated. Immunohistochemically, all cases were STAT6 positive. Age, sex, tumour size, location, hypercellularity, mitotic activity, presence of necrosis, hemorrhage, moderate to high-grade nuclear pleomorphism, recurrence, death, and time for recurrence were noted. Tumours were graded according to WHO2016 and WHO2021 classifications. Recurrence-free and overall survival statistics were applied. Results: The mean age was 37 (14-51) with M:F ratio of 12:11. Tumours had intracranial (n=19) and spinal (n=4) locations; sizes ranged from 2 to 7 cm with a mean of 4,2 cm. Tumours were classified by WHO2021 as grade 1 (n = 12), 2 (n = 6), or 3 (n = 5), and by WHO2016 as grade 1 (n =4), grade 2 (n=8), or grade 3 (n=11). Necrosis was present in 7 (30%). Recurrence occurred in 10 (44%) patients within a mean of 5.6 years, 7 of which were dead during follow-up. On univariate analysis, neither of the above-mentioned parameters nor grading schemes were associated with recurrence-free or overall survival. Conclusion: According to our data, morphological and clinical parameters, as well as WHO grading schemes, failed to stratify this family of tumours accurately. OFP-13-004 Response to regorafenib of recurrent glioblastoma. A clinical and NGS study M. Martini*, Q.G. D’Alessandris, T. Cenci, V. Fiorentino, L. Lau- retti, M. Balducci, R. Pallini *Università degli Studi di Messina, Italy Background & objectives: Predictive factors for response to regorafenib in recurrent glioblastoma, IDH-wildtype, are scarcely recognized. The objective of this study was to identify molecular predictive factors for response to regorafenib using a clinically available platform. Methods: We analysed a prospective cohort of 30 patients har- bouring recurrent glioblastoma, IDH-wildtype, and treated with regorafenib. Next-generation sequencing (NGS) analysis was per- formed on DNA extracted from paraffin-embedded tissues using a clinically available platform. Moreover, MGMT methylation and EGFRvIII expression analyses were performed. Results: Six-month progression-free survival (PFS) was 30% and median overall survival (OS) was 7.5 months. NGS analysis revealed a mutation of EGFR pathway in 18% of cases and a mutation in the mitogen-activated protein-kinase (MAPK) pathway in 18% of cases. In the remaining cases, no mutations were detected. MAPK pathway mutated patients had a poor response to regorafenib treatment, with a significantly shorter PFS and a nonsignificantly shorter OS compared to EGFR-mutated patients (for PFS, p=0.0061; for OS, p=0.1076). Multivariate analysis confirmed that MAPK pathway mutations independently predicted a shorter PFS after regorafenib treatment (p=0.0188). The negative prognostic role of MAPK alteration was reinforced when we combined EGFR-mutated with EGFRvIII-positive cases. Conclusion: Recurrent glioblastoma tumours with an alteration in MAPK pathway could belong to the mesenchymal subtype and respond poorly to regorafenib treatment, while EGFR-altered cases have a better response to regorafenib. We thus provide a molecular selection criteria easy to implement in the clinical practice. OFP-13-005 Digital image analysis is a powerful tool to demonstrate the prognostic impact of proliferation assessed with Ki67 and PHH3 in meningeal solitary fibrous tumours H. Nihous, C. Bouvier*, B. Lemarié, D. Figarella Branger, N. Macagno *Department of Pathology, Timone Hospital, France S53