ECP 2023 Abstracts

S191 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 months the patient returned with relapse of a polypoid skin tumour measuring 65mm with satellite lesions. He underwent a wide excision. Results: On gross section, the tumour was whitish, solid extending in depth up to 25mm. Microscopically, it consisted of medium sized monomorphic tumour cells with a “salt and pepper” chromatin pattern and brisk mitotic rate and cells with squamoid appearance. The neo- plastic population was arranged in solid and trabecular structures with central necrosis, often with retraction artefact. The tumour cells had neuroendocrine differentiation as evidenced by their immunophenotype (CK8/18+, CK20+, CD56+, Synaptophysin+, Chromogranin-A+) and squamous differentiation in areas of p63 and CK5/6 expression. Ret- rospective study of the first lesion revealed similar morphology and immunophenotype with an in-situ component. The final diagnosis was MCC with divergent squamous differentiation. Conclusion: MCC with divergent squamous differentiation is a diag- nostic challenge for the general pathologist. It’s a rare MCC subtype with only a few reported case studies or small case series. Recent research supports that the neuroendocrine and squamous component share genetic common profiles, while proposing the Rb-deficient subset of squamous cell carcinomas as the possible source of the divergent MCCs. Further research is warranted to better understand the pathogenesis, clinical behaviour, and optimal treatment approaches for this rare sub- type of MCC. E-PS-05-045 Correlation between histologic subtype and location of basal cell carcinoma (BCC) in Greek population N. Stavrinou*, S. Pantelakos, C. Vourlakou, V. Damaskou, I.G. Panayiotides *Department of Pathology, Evaggelismos General Hospital Athens, Greece Background & objectives: BCC is the most common type of skin cancer. Due to the high incidence of BCC in countries with high sun exposure (eg Mediterranean), the study of the correlation between his- tologic type and location of BCC is of particular interest. Methods: In order to investigate the correlation between histologic subtype and location of BCC, we examined 661 BCCs. Statistical analysis was performed using IBM-SPSS. Distribution was divided into two categories: head & neck and trunk & extremities. Histology was divided into 9 categories according to W.H.O. classification. Other data, such as patient’s age and gender were also taken into account. Results: 58.1% of the patients were men; the median age of the patients was 73 ± 12.3 for men and 71 ± 12,1 for women. The most common subtype was nodular BCC (22%), most often located on the nose, which constitutes 31.4% of the total number of cases located in the head and neck area. Superficial spreading BCC arose more frequently on the back (37%). In our study, BCC in general was noted mostly between 71-80 years of age, whereas the infiltrative subtype was predominantly found in patients aged over 81 (69.2%). Conclusion: The results of this study of a Greek population are simi- lar to those of studies performed in other countries. In most studies, nodular BCC constitutes the most common histologic subtype, usually located in the head and neck. However, studies performed in Australia and in France showed that the most common histologic subtype is superficial spreading BCC and the distribution which was mostly noted is at the back and head and neck respectively. E-PS-05-046 Cutaneous epithelioid angiomatous nodule (CEAN): a diagnostic pitfall A. Syrnioti*, G. Raptou *Department of Pathology, School of Medicine, Aristotle University of Thessaloniki, Thessaloniki, Greece Background & objectives: Cutaneous epithelioid angiomatous nodule (CEAN) is a rare, recently recognized, benign vascular proliferation of the skin that can pose significant diagnostic challenges due to its histological similarity with both benign and malignant vascular tumours, including epithelioid angiosarcoma, haemangioendothelioma, and haemangioma. Methods: Here we describe a case of a CEAN, in a 24-year-old male, who presented with a solitary, 8-mm well-circumscribed, light brown nodule on the back. The nodule was excised and sent for histopatho- logic examination. Hematoxylin-eosin and immunohistochemical stained sections were examined. Results: Microscopic examination revealed a well-circumscribed nod- ular lesion, located in the upper and mid-dermis. The lesion was com- posed of solid sheets of medium-sized epithelioid cells with abundant eosinophilic cytoplasm and ovoid, vesicular nuclei with conspicuous nucleoli. A small number of mitoses was focally detected, without sig- nificant nuclear atypia or pleomorphism. In the periphery of the lesion, vascular formations were also present. The overlying epidermis was ulcerated. On immunohistochemical evaluation, the lesional cells were diffusely positive for ERG, focally positive for CD34, and negative for Human herpes virus-8 (HHV-8). A moderate number of SMA-positive pericytes were also observed within the lesion. Based on these findings, the diagnosis of CEAN was established. Conclusion: CEAN is an unusual entity that can often lead to misdi- agnosis. The absence of atypical mitoses, significant nuclear atypia, necrosis, and infiltrative growth can help distinguish it from more omi- nous epithelioid vascular proliferative lesions and avoid unnecessary treatment. E-PS-05-047 Primary cutaneous melanoma with rhabdomyoblastic differentia- tion – histopathological and immunohistochemical analysis of an extraordinarily rare malignancy D. Tapoi*, A. Dumitru, A. Ciongariu, D. Chetroiu, S. Gradinaru, C. Alius, M. Costache *University Emergency Hospital, Romania Background & objectives: Melanoma is a heterogeneous disease with widely variable histopathological, immunohistochemical, and molecu- lar features. Cutaneous melanomas can undergo divergent differentia- tion, displaying immunohistochemical and ultrastructural features of other cell lineages. Even though rare in primary lesions, such cases represent major diagnostic challenges. Methods: Primary cutaneous rhabdoid melanomas are unusual entities, more commonly encountered in metastatic cases. Furthermore, true rhabdomyoblastic differentiation of primary cutaneous melanomas is extraordinarily rare, as rhabdoid melanomas usually fail to express immunohistochemical myogenic differentiation. The aim of our study is to gain further insight into this peculiar entity by evaluating histo- pathological and immunohistochemical characteristics as well as dif- ferential diagnosis. Results: We report the case of a 42-year-old male with an ulcerated nodular lesion on his posterior thorax. After surgical removal, histo- pathological examination revealed a proliferation of neoplastic cells with a pseudo-alveolar growth pattern, ulcerating the epidermis and invading the subcutaneous tissue. The tumour cells were large, polygo- nal with abundant eosinophilic cytoplasm and eccentric nuclei with prominent nucleoli. Multinucleate cells were also present. The primary differential diagnoses were alveolar soft part sarcoma and rhabdomyo- sarcoma. Immunohistochemically, the cells were completely negative for HMB45, focally positive for desmin and myogenin and diffusely positive for vimentin, SOX10 and Prame. Based on these features, the diagnosis of primary cutaneous melanoma with rhabdomyosarcoma- tous differentiation was established. Conclusion: Rhabdoid features in primary cutaneous melanomas have rarely been described. These tumours usually keep their melanocytic