ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 Background & objectives: Instersticial Mycosis Fungoides (IMF) is a rare histological variant of Mycosis Fungoides that may mimic inflam- matory dermatoses as granuloma annulare, morphea and interstitial granulomatous dermatitis. The cases of IMF from our institution have been reviewed in order to characterize it. Methods: Four cases diagnosed with Interstitial Mycosis Fungoi- des (IMF). All clinical, histopathologic and immunohistochemi- cal variables were collected. All of them were men, with a mean age of 61 years old (range 42-80) with previous diagnosis of classic MF and clinical symptoms of poikiloderma and plaque. Results: Three patients presented annular lesions and nodules after two and four years of follow-up in one and two cases, respectively, which were biopsied. The fourth patient started with chronic purpura pigmentosa lesions and after six years of evolution, the annular lesions also appeared. In all cases, a perivascular and interstitial lymphocytic infiltrate was observed, accompanied by macrophages (CD163 positive). These were arranged in a palisade, simulating a granuloma annulare. Mucin deposition was also observed. The lymphoid infiltrate was CD4 positive. TCR-gamma gene was rearranged in all the cases, showing a monoclonal population. Conclusion: -Diagnosis of IMF is challenging, as it mimics granuloma annulare clinically and histologically. -In cases with previous MF, IMF is associated with clinical modifications. -IMFs display a double population of lymphocytes and mac- rophages, which makes them difficult to observe/distinguish. - It is necessary to know this rare variant in order to recognize it. E-PS-05-004 Clear cell variant of atypical fibroxanthoma and pleomorphic dermal sarcoma: molecular characterisation of two cases J. Coelho Lima*, J. Bruty, J. Watkins, H. Liu, R. Price, N. Stefanos *Department of Pathology, University of Cambridge, United Kingdom Background & objectives: Atypical fibroxanthoma (AFX) and pleo- morphic dermal sarcoma (PDS) are unusual cutaneous tumours. The molecular profile of the rare clear cell (cc) variant is unknown. We present key morphologic and molecular features of two ccAFX and ccPDS cases. Methods: Total genomic DNA was extracted from formalin-fixed paraffin-embedded tumour tissue and next generation sequenc- ing (NGS) was performed using the TruSight Oncology 500 assay (Illumina, CA, USA). This platform enables profiling of 523 genes for identification of DNA variants, quantification of microsatellite instability (MSI), and tumour mutational burden (TMB). Variant annotation was performed using the Molecular Tumour Board Por- tal (MTBP). Results: Both tumours presented as nodular lesions on the scalp of elderly males. Microscopically, they comprised intradermal sheets of cells with abundant pale to clear cytoplasm, severely pleomorphic nuclei, and frequent mitoses. The ccPDS extended into the deep subcutis. Neoplastic cells expressed CD10 strongly and diffusely and lacked expression of other markers. Both tumours showed high TMB (ccAFX: 67.9mt/mb; ccPDS: 105.3mt/mb) and no significant MSI. Loss-of-function mutations in the TP53, CDKN2A, and NOTCH1 genes were detected in both cases, similarly to other AFX and PDS variants. TERT promoter and NOTCH2 mutations were present in the ccAFX case only whereas an APC mutation was present in ccPDS. No tumour recurrence was observed. Conclusion: Clear cell AFX and PDS seem to share fundamental molecular driver events. Their molecular profile is also similar to that described in more common variants. Whilst no unique mutational profile was identi- fied in our cases, presence of the genetic abnormalities described herein may increase the level of confidence in diagnosing these lesions. Adverse histologic features such as tumour necrosis, lymphovascular invasion, and extension into deep subcutis still remain essential for distinction between AFX and PDS. E-PS-05-005 Eruptive junctional melanocytic naevi associated with cutane- ous mastocytosis, a rare case report F. Kubba*, A.T. Gradassi *Department of Pathology, Ealing Hospital, London North West University Healthcare NHS Trust, United Kingdom Background & objectives: A 32 year old Caucasian male presented with red maculopapular rashes following psychological stress, triggered by alcohol, coffee and hot water exposure, distributed all over the body and subside leaving red papules. No diarrhoea, headaches or flushing symptoms were reported. Methods: There was dermographism and macular rashes induced by scratching on the abdomen, back and arms. Skin punch biopsies from the abdomen and the arm showed SOX10 positive small junc- tional nonpigmented melanocytic nests. Toludine blue and CD117 showed increased dermal mast cells. Bone marrow biopsy showed no C-Kit mutation and serum tryptase was normal. No hepatosple- nomegaly/lymphadenopathy was seen on CT scan. Results: Around 10 similar cases have been reported, including a case report by Danotti et al. There is prevalence for female patients. CD117 is thought to be expressed in 29% of melanomas, which may also have therapeutic implications. In our case CD117 was negative in the melanocytes. Hägglund et al reported an increased risk of melanoma in patients with systemic mastocytosis. The C-Kit proto-oncogen codes for the transmembrane tyrosine kinase receptor of the stem cell factor (SCF). Increased CSF induces mel- anocyte proliferation, melanin pigment production and deposits in keratinocytes. The papules were around a millimetre in size and none underwent recent change. This was an incidental unexpected finding on histopathology. Conclusion: We presented a rare case of eruptive melanocytic naevi associated with cutaneous mastocytosis in a young man, which was an incidental histology finding. This rare condition con- firms the similar pathogenesis between the mast cells and melano- cytic naevi, related to the increased SCF stimulation. Such patients need close follow up to ensure early diagnosis of melanoma. They also need to be fully investigated to exclude systemic mastocytosis. They are offered symptomatic relief of their itching and rashes. E-PS-05-007 Metatypical basal cell carcinoma overlying a dermatofibroma: an association never described before H. Trihia*, P. Manikis *Pathology Department Metaxa Cancer Hospital, Greece Background & objectives: Dermatofibroma (DF) is a skin tumour, mostly located on the limps. The overlying epidermis shows simple hyperplasia to basal cell carcinoma (BCC). We report a tumour consist- ing of DF and metatypical BCC in the outer surface of the left forearm. Methods: A 84-year old woman presented to our dermatol- ogy clinic for evaluation of a lesion on her left posterior arm. She was uncertain as to its duration and she denied any pain or bleeding. Physical examination revealed a 13mm raised circum- scribed smooth, lobulated skin nodule, with solid, whitish and S207