ECP 2023 Abstracts

S182 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 melanomas. The aim of this study is to detect the incidence of nevus- associated LMM (NALMM) and its relationship with histopathologic aspects. Methods: We conducted a retrospective observational study from his- topathology reports of patients treated with Grenz rays (GR) Bucky, for lentigo maligna (LM) and lentigo maligna melanoma (LMM), at the dermatology department, Karolinska University hospital, Sweden, between January 1, 2004 to December 31, 2016. A total of 348 reports were reviewed for the presence of benign melanocytic nevus, with the LM/LMM Results: Nine patients (21%) in the NALMMgroup had more than 50 mel- anocytic nevi compared to 13 patients (8%) from the control group. Twelve patients (27%) in the NALMM group had previously removed at least one dysplastic nevus (p= 0.04) and 11 patients (26%) had been diagnostic with another melanoma, of which 7 of those (64%) were also nevus-associated melanoma. In the study group, two male patients, with facial in situ lesions with deep follicular distribution (1,6 mm and 1,7 mm), developed mela- noma metastasis. One patient was treated with cryotherapy, before surgical removal, and 10 years after treatment developed a brain metastasis, with the same molecular signature as the initial LM. Conclusion: When focusing on LMM we found discrepancies com- pared to previous reports. Three possible explanations for this sample variation can be due to the interpretation of these intradermal micro nevi. The first one, they are considered incidental, a collision phenom- enon; the second, the micro nevi are hidden between histological cuts; and the third, they are considered an invasive part of the LMM since they can present challenges difficulty when trying to differentiate such nevi cells from melanoma. E-PS-05-011 Three cases of cutaneous AL-amyloidoma/ primary cutaneous marginal B cell lymphoma, associated to Sjögren syndrome. Utility of fluorescence microscopy in the identification of dermal amyloid A. Córdoba*, I. Fernandez, C. Llanos, J.I. Yanguas, C. Cerezo, M.R. Mercado, D. Guerrero-Setas *Hospital Universitario de Navarra, Spain Background & objectives: We hypothesize that the association between cutaneous AL-amyloidoma and Sjögren syndrome (SS) fur- ther supports the biological link between the first one and pc Marginal Zone Lymphoma. Detection of amyloid in the dermis under fluores- cence microscopy (FM) might be very useful. Methods: We report three patients with SS (two women, one man), aged 67-77 years-old. Infiltrated plaques in lumbar and leg skin were observed, being unique in two patients and multiple in the third one. Results: Histologically, deposits of amyloid were observed in the papil- lary and reticular dermis, associated with a sparse perivascular infiltrate of lymphocytes and plasma cells. Congo red resulted lightly positive. Amyloid substance gives a bright red fluorescence stained with Congo red in paraffin-embedded tissue sections examined under FM with Texas Red (TR) and double FITC/TR filters, confirming the diagnosis with high specificity. We have observed light chain restriction in two cases, confirming the clonal nature by B rearrangement in two cases. Conclusion: The use of FM with TR and double FITC/TR filters is useful to confirm the diagnosis of cutaneous AL-amyloidoma. Despite the overall rarity of this disease, an association has been established with chronic autoimmune diseases, especially SS. It might be hypothesized that in a small subset of pcMZL with exten- sive plasmacytic differentiation, the monotypical immunoglobu- lin light chains find the necessary physicochemical conditions to undergo extensive amyloidization. SS is the autoimmune disorders associated with the highest risk of lymphoma, particularly MZL. E-PS-05-012 Melanocytic spitzoid lesions with FISH-positive abnormalities. BRAF V600E, PRAME and BAP1 assesment A. Córdoba*, C. Cerezo, C. Llanos, G. De Lima, M. Montes, J.I. Yanguas, D. Guerrero-Setas *Hospital Universitario de Navarra, Spain Background & objectives: Melanocytic spitzoid lesions are difficult to diagnose, with lack of concordance among experts. Here we evaluate the usefulness of molecular analysis (FISH and BRAF mutation) and new immunohistochemical (IHC) markers (PRAME and BAP1) for diagnosis and classification of melanocytic lesions. Methods: The group of study consists of all spitzoid melanocytic lesions with atypia diagnosed in the period 2018-2022 in our institution (n=42 cases). FISH was performed by using the Melanoma Multiprobe set composed of RREB1 (6p25), MYB (6q23), CCND1 (11q13) and p16/ CDKN2A (9p21) genes. BRAF p.V600E mutation study was analysed by qPCR and PRAME and BAP1 expression was evaluated by IHC. Results: Abnormalities were observed in 17 (40.4%) FISH-positive cases; 3 out of 17 cases displayed two abnormalities. p16/CDKN2A abnormalities were the most prevalent, with homozy- gous (11, 64.7%) or heterozygous loss (3, 17.6%). MYB, RREB1 and CCND1 were gain in 3 (17.6%), 2 (11.7%) and 1 case (11.7%), respectively. BRAF p.V600E mutation was observed in 9 (52.9%) of these 17 cases. 5 cases with homozygous p16 loss displayed this mutation. PRAME was positive in 4 BRAF-mutated cases whereas the three BAP1-negative cases showed BRAF mutation. Conclusion: - We observed that FISH-positive cases showed high incidence of BRAF mutation and PRAME expression, alterations associated to melanoma or Spitzoid melanoma. -The integration of these diagnostic tools could help in the differential diagnosis in spitzoid melanocytic lesions which could allow to differenti- ate nevus (FISH-negative), melanoma (FISH-positive + PRAME-posi- tive) and Spitz melanoma (FISH-positive + p16 loss + BRAF-positive + BAP1 negative). E-PS-05-013 Superficial acral fibromyxoma – rare lesion or unknown entity? S. Costache*, A. Baltan, A. Gont, A. Chefani, M. Sajin, C. D’Arrigo *University Emergency Hospital Bucharest, Poundbury Cancer Insti- tute, Romania Background & objectives: Superficial acral fibromyxoma (SAF) is a rare, slow growing, benign mesenchymal tumour that was first described by Fetsch et al. in 2001. It typically occurs on the fingers and toes, particularly in the nail bed or under the nail. Methods: We present two cases of SAF, one of a 63 year old male on second toe right foot and the other of a 62 year old female on left index. Both lesions were sampled, fixed in formalin, processed and embedded in paraffin and further studied using conventional stains and ancillary immunohistochemical (IHC) studies. Results: Grossly both lesions have a firm, solid, grey and uniform cut surface. Histologically they consist of a large, round, well defined and non encapsulated spindle cell, deep seated dermal lesion with a small overlying grenz zone. The lesion shows a moderately cellular population of bland fibroblastic cells each surrounded by a small amount of myxoid ground substance. These cells are in close association with relatively thick collagen bundles and form randomly arranged loose fascicles with inconspicuous thin, short and curved vessels. There is no necrosis and mitoses are not a feature. IHC studies show that the component cells are diffusely CD34 positive and S100, EMA, SMA and Desmin negative. Conclusion: SAF is usually diagnosed using IHC studies and the main differential diagnosis includes superficial angiomyxoma, myxoid neurofi- broma and perineurioma. Due to its rarity and being recently described,