ECP 2023 Abstracts

S295 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Results: A 53-year-old woman presented with a parotid gland mass. A category IVB neoplasm was reported by FNAC. The patient was submitted to superficial parotidectomy. The tumour was well-circumscribed and encapsulated. It was com- posed of monotonous cells arranged in anastomosing trabeculae, with acinar and microcystic spaces. Beading of tumour cells, charac- teristically described in CAs, was observed. The background stroma was loose with oedematous-haemorrhagic areas. No conventional PA component was identified. FISH analysis revealed HMGA2 rear- rangement, supporting PA diagnosis. A recent study described a series of PA with CA-like morphology with recurrent HMAG2 fusion, supporting that they are distinct from CA of minor salivary glands and a “monomorphic variant” of PA. Conclusion: PAs have a wide morphological spectrum that encom- passes monomorphic tumours. PAs with a CA-like morphology are a diagnostic challenge, especially when no conventional PA compo- nent is present. Knowledge of this distinct variant and, in this setting, genetic testing for HMGA2, gene is of great value. This case increases the awareness of this atypical presentation, helping to avoid diagnostic difficulties. E-PS-12-053 Collision tumour of sclerosing microcystic adenocarcinoma and squamous cell carcinoma of the tongue: an exceptional case report O. Sahin*, M.H. Karabulut, Y.K. Duymaz, I.E. Zemheri *University of Health Sciences, Umraniye Training and Research Hos- pital, Department of Pathology, Turkey Background & objectives: Sclerosing microcystic adenocarcinoma (SMA) is a rare type of malignant tumour arising in the head and neck mucosa, resembling microcystic adnexal carcinoma (MAC). Here, we report a unique case of simultaneous co-occurrence of SMA and squa- mous cell carcinoma (SCC). Methods: A 64-year-old male with a one-year history of a solid lesion on the right side of the tongue presented to the clinic. Clinical exami- nation and magnetic resonance imaging (MRI) revealed a heterogene- ously contrasted lesion with irregular contours. The lesion had also invaded the left genioglossus muscle. Tru-cut biopsy was performed. Subsequently, the patient underwent hemiglossectomy. Results: Tru-cut biopsy revealed MAC. Upon evaluation of the resected specimen, gross examination disclosed ulcero-infiltrative tumoral lesions. Histological examination revealed that the tumour was comprised of 75% poorly differentiated SCC and 25% SMA. The SMA segment formed tubules within the dense fibrous stroma and exhibited deep infiltration. Two types of cell populations were observed: luminal cells, which showed bland nuclear morphology and expressed cytokera- tin 7 (CK7) and carcinoembryonic antigen (CEA), and myoepithelial cells, which expressed P63 and P40. Both cell populations were nega- tive for SOX10 and CD117. The Ki67 proliferation index was 5% in SMA and 40% in SCC. Perineural invasion was present in both SMA and SCC. Conclusion: SMA is a new entity included in the 5th edition of the World Health Organization (WHO) classification of Head and Neck Tumours, and a rare type of malignant tumour should be differenti- ated from MAC. This case report presents a novel contribution to the literature by documenting the coexistence of SMA and another tumour, a finding that has not been previously reported. E-PS-12-054 Low-grade nasopharyngeal papillary adenocarcinoma with breast metastasis: a unique case report O. Sahin*, M.H. Karabulut, S. Cetin, Y.K. Duymaz, I.E. Zemheri *University of Health Sciences, Umraniye Training and Research Hos- pital, Department of Pathology, Turkey Background & objectives: Low-grade nasopharyngeal papillary ade- nocarcinoma (LGNPPA) is rare indolent tumour that originates from nasopharyngeal surface epithelium. It has favourable prognosis, with no previously reported cases of metastasis. In this report, we document the first instance of metastatic LGNPPA in the literature. Methods: A 41-year-old female patient presented with a nasopharyn- geal mass and was evaluated at an external facility for carcinoma of unknown primary origin. Upon the biopsy, the patient was inaccurately diagnosed with papillary thyroid carcinoma, which subsequently led to the initiation of chemotherapy treatment. The patient was then referred to our centre for verification of the histopathological diagnosis. Results: Clinical and radiological examinations revealed a mass in the nasopharynx, causing destruction to the skull base. Microscopically, adenocarcinoma with a papillary configuration invading the bone tissue was observed. Immunohistochemical staining was positive for TTF1, cytokeratin, and EMA and negative for thyroglobulin and PAX8. Dur- ing follow-up, a suspicious lesion in the breast was detected on posi- tron emission tomography (PET-CT), prompting magnetic resonance imaging (MRI). A subsequent tru-cut biopsy revealed adenocarcinoma with a papillary and tubular pattern. Histopathological and immuno- histochemical findings confirmed the presence of metastatic LGNPPA. Conclusion: In this unique case report, we underscored the importance of LGNPPA in the differential diagnosis of nasopharyngeal tumours, highlighting the challenges in differentiating LGNPPA from papillary thyroid carcinoma (PTC) owing to overlapping morphological and immunohistochemical features. This report presents the first docu- mented instance of LGNPPA metastasis. Future research should focus on elucidating the molecular and genetic characteristics of LGNPPA and its metastatic potential, which may ultimately reshape our percep- tion of the behaviour of what is known as an "indolent tumour.” E-PS-12-055 Two paediatric immature teratoma cases located in the head and neck region K. Simsek*, A. Yavuz, G. Karaguzel, N. Yaprak Barıt, I.E. Gurer *Akdeniz University Department of Pathology, Turkey Background & objectives: Teratomas with immature tissues and with various quantities of mature tissues are referred to as immature terato- mas. Midline localization is where extragonadal teratoma frequently manifests itself. We present two paediatric immature teratoma cases located in the head and neck region. Methods: Pathological examination was performed by routine hema- toxylin-eosin and for the immunohistochemical staining Pan CK, CD56, synaptophysin, GFAP and Ki67 immunohistochemical mark- ers were used. Patients’ AFP and Beta-Hcg levels were measured as of biochemical markers. MRI was used as radiologic imaging. Results: Case 1 A 9-day-old female newborn was admitted with dyspnea and stridor. Physical examination showed a mass on the cervical region. The patient was operated and histopathological examination revealed teratoma morphology which contains three germ layers. In three low-power fields, an immature teratoma component was seen that comprises primitive neuroectodermal cells. Case 2 A female newborn presented with dyspnea, cleft palate and para- pharyngeal mass. After the resection of this mass, histopathological findings were compatible with immature teratoma. During the follow-up both of the patients, they did not experience any recurrence or metastasis in 3 and 24 months, respectively. The patients’ AFP levels were within the normal range during these periods. Conclusion: In paediatrics, teratomas are the most prevalent histo- logic type of germ cell tumours. There are two types of teratomas; mature and immature type. Histopathological examination of immature