ECP 2023 Abstracts

S285 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 and immunohistochemical data, along with the clinical history of the patients, were analysed. Clinical evolution was reviewed as well. Results: We have found 10 cases, all of them in men, with a mean age of 71. Of the 10 cases, two were outpatient clinics where the prepara- tions were returned. The remaining 8 microscopically presented mostly ulcerated surface epithelium. In 4 cases the tumour presented epithelial differentiation in hematoxylin-eosin. One case presented epithelial dif- ferentiation only IHC for CK AE1/AE3. The remaining 3 did not pre- sent epithelial differentiation both by morphology and by IHC, but the patients had a history of SCC in the same location. One case presented mesenchymal differentiation to high-grade chondrosarcoma, the rest the sarcomatoid component was composed of spindle cells arranged in sheets and intertwined bundles. Conclusion: SCC is a tumour in which differential diagnosis includes entities like sarcomas, melanoma, fibromatoses, and leiomyoma, to name a few. When dealing with these biopsies, we must first consider whether we are dealing with benign or malignant entities and request a directed IHC panel that includes epithelial, melanocyte, and muscle markers, always keeping in mind that they may not express them. In the end, be aware that a spindle cell tumour in this location is SCC unless proven otherwise. E-PS-12-011 An aggressive sinonasal tumour with neuroepithelial differentia- tion: olfactory carcinoma M. Bundele*, L. Rooper *Tan Tock Seng Hospital, Singapore Background & objectives: 55-year-old Chinese male presented with right nasal cavity mass. MRI showed intracranial extension with involvement of cribriform plate raising possibility of olfactory neuro- blastoma. He had a previous history of undifferentiated nasopharyngeal carcinoma, treated with chemoradiation 7 years before. Methods: Histology showed high grade infiltrative tumour featuring neuroectodermal component in nested/ lobulated/ solid architecture within vascular stroma and prominent rosettes with intermixed well- formed glands. Tumour was diffusely positive for cytokeratin AE1/3 with focal stain- ing for synaptophysin and chromogranin and CD56. CK7 was focally positive. INI1 was retained. CK20, CDX2, TTF1, p40, CD99, WT1, FLI1, SOX10, S100 and HMB45 were negative. Results: Further in situ hybridization for EBV encoded RNA was negative. The tumour recurred in less than a month and showed mainly solid (blastomatous) component on histology. Blastomatous and rossettoid areas raised the differentials of other small round blue cell tumours such as neuroendocrine tumours including neuroendocrine carcinoma, olfactory neuroblastoma, prim- itive neuroectodermal tumour, INI-1 deficient carcinoma and terato- carcinosarcoma, however overall morphology and immunostaining excluded these differentials. No stromal or foetal elements that define teratocarcinosarcoma were seen. A metastatic poorly differentiated adenocarcinoma was also excluded. Post recurrence resection, patient developed orbital apex syndrome, developed dural metastasis, underwent chemotherapy but finally suc- cumbed to disease within 10 months of the initial diagnosis. Conclusion: We present a case of aggressive sinonasal tumour with a neuroepithelial phenotype involving cribriform plate. The term ‘Olfactory carcinoma’ has been prominently used in previous litera- ture for tumours with similar morphology. The progenitor stem cell- Olfactory basal cell with potential for differentiating into multiple lineage is believed to be precursor cell. Further clinicopathologic and molecular analysis of these tumours with neuroepithelial phenotype should be considered to better define them, to facilitate more complete understanding of their classification, pathogenesis, and treatment. E-PS-12-012 Recidivant chordoma of the clivus with progression to dedifferenti- ated subtype: a case report on a rare entity G. Carrola*, A.P. Rodrigues, D. Sá, F. Sousa Vieira, J.R. Brandão *Centro Hospitalar Universitário de Santo António, Portugal Background & objectives: Dedifferentiated chordoma is a very rare entity, representing the least common subtype of chordomas and also the most aggressive. Our aim is to review a case initially diagnosed with a conventional chordoma that progressed to the dedifferentiated subtype during follow-up. Methods: We reviewed the history of an 84-year-old female patient with a previous diagnosis of conventional chordoma located at the skull base. The patient was submitted to surgical treatment and adjuvant stereotactic radiotherapy. Nevertheless, several recurrences occurred, so multiple re-excisions were necessary during a five-year period. Histopathological and immunohistochemical investigation of these specimens was conducted. Results: Histological examination of the first recurrence showed a multinodular neoplasm composed of typical physaliferous cells set in a myxoid stroma and a 7mm focus of undifferentiated spindle cells with high mitotic rate. Immunohistochemistry demonstrated normal positiv- ity for CAM5.2, vimentin, S100, CD99, INI1 and negativity for, cal- ponin, SMA, p63, and GFAP. The undifferentiated component showed loss for all immune stains. Proliferative index (Ki-67) in hotspot areas was 5% in the conventional subtype and 30-40% in the sarcomatous component. We signed out as recidivant dedifferentiated chordoma. After the second re-intervention, analysis showed similar histopatho- logical features, this time with a greater undifferentiated component, with high mitotic rate and focal necrosis. Conclusion: Dedifferentiated chordoma is extremely rare, having few cases reported in literature. It represents the most aggressive subtype of chordomas and treatment is challenging. Total excision with free margins is still the gold standard, combined with adjuvant radiother- apy. Recurrence, with the need for reintervention, and progression to a higher volume of the dedifferentiated component can lead to less favourable outcomes. Overall, poor prognosis and poor quality of life is expected, particularly in old females with skull base involvement. E-PS-12-013 Methodology for fluorescence signal analysis in head and neck can- cer surgical specimen after indocyanine green intravenous injec- tion: MAGNOLIA project O. Casiraghi*, G. Marguerit, P. Khneisser, N.I. Ben Romdhane, I. Breuskin, S. Temam, P. Gorphe, M. Abbaci *Gustave Roussy, Université Paris-Saclay, France Background & objectives: Fluorescence guided surgery for tumour tis- sue resection or lymph node identification is described mainly with Indo- cyanine Green (ICG). We are conducting a clinical trial after ICG injection for intraoperative control of surgical margins in head and neck cancers. Methods: For now, five patients diagnosed with squamous cell carcinoma and indication for oral surgery (T1-T2) were included (5/60). They received ICG at 0.2 mg/kg , 45 min prior tumour incision. After fixation, the patholo- gist sectioned the surgical specimen every 3mm. Fluorescence signal from each tissue section was recorded according to standardized conditions with Spectrum hand-held Near-Infra-red (NIR ) fluorescence camera. Results: We developed a methodology based on tiles technique approach and threshold values, to analyse fluorescence signal in each tissue section containing or not cancer tissue. The data were correlated with final histology to measure intensity and distribution of fluores- cence signal according to tissue histology. This strategy made it pos- sible to determine the percentage of false negatives, false positives, true negatives and true positives within regions of interest of 4mm2 in each sections, and to evaluate the global concordance rate for each patient.