ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 Conclusion: Although future studies on larger series of patients are necessary, LC-OCT, based on these preliminary findings, may represent a promising tool in inflammatory skin disorders with potential applications including enhanced diagnosis, biopsy guid- ance, follow-up and treatment monitoring. OFP-07-008 The challenging differential diagnosis of ALK-positive cutane- ous lesions, a case series L. Keulen*, J. Liu, K. Dewinne, P. Pauwels, V. Siozopoulou *Department of Pathology, Antwerp University Hospital, Edegem, Belgium Background & objectives: ALK-positive cutaneous lesions com- prise epithelioid fibrous histiocytoma (eFH), ALK-positive non- Langerhans cell histiocytosis (non-LCH) and Spitz lesions. These are rare entities, sometimes with overlapping histologic features, hence their differential diagnosis can be challenging. Methods: We collected a series of 14 patients with ALK-positivity on immunohistochemistry (IHC). Two case were diagnosed as non- LCH, 4 as eFH and 8 as Spitz lesions. IHC with the same ALK clone (5A4) was implemented in all cases. A NGS-RNA Oncomine Focus Assay was performed in the 6 non-Spitz lesions. We com- pared the morphological, immunohistochemical and molecular findings. Results: The median age for the non-LCH was 16,5 years(all females), for the eFH 40 years(females=males) and for the Spitz lesions 20 years(75% females). The entities shared common morphologic features: circumscribed or ill-defined lesion, spindle or epithelioid cell morphology, fascicular, storiform or nodular growth pattern. On IHC, all tumours demonstrated diffuse and strong ALK expression. The histiocytic tumours were at least partially positive for CD68. S100 was focally expressed in some eFH, whereas SOX 10 and/or melan-A were confined to the Spitz lesions. No other IHC stainings aided in the differential diagnosis. Molecular analysis in the non-Spitz lesions showed a SQSTM-ALK fusion in 2 eFHs and a KIF5B-ALK in a non-LCH. Conclusion: We present a series of ALK-positive non-LCH, eFH and Spitz lesions. These three entities show overlapping mor- phological features. However, Spitz lesions are characterized by SOX10 and/or Melan-A positivity, which is not seen in eFHs and non-LCH. Still, for the histiocytic entities, IHC is not able to nar- row down the differential diagnosis. Additional molecular testing may help, since specific ALK fusion partners have been demon- strated in certain entities. OFP-07-009 Melanoma in situ with regression O. Gokoz, D. Ateş Özdemir, H.G. Terzioglu* *Hacettepe University, Turkey Background & objectives: Regression in melanoma in situ (MIS) has been reported but not well studied. Defining the clinical and histopathological features of cases with regression can help work- up of patients and be a step to determine the value of regression in prognosis. Methods: Ffifty-six cases with a diagnosis of MIS in 2014-2022 were retrieved from the archives and retrospectively examined for the type of MIS, presence of melanophages, fibrosis, vascular pro- liferation and/or vertically arranged vessels, presence and degree of inflammation, elastosis, presence of folliculotropism, immunohis- tochemical stainings and surgical margins. Demographic features, clinical history and follow-up findings were recorded. Results: There were 40 patients with regression, 19 males and 21 females with an average age of 61.8 and 51.3 respectively. Head and neck were the most frequent localization (45%). The mostly seen MIS type was lentigo maligna (62.5%), MIS developing on dysplastic nevus being the second (20%). Melanophages together with inflammation were present in 71.4% of cases. Folliculotropism was seen in 55%, vascular proliferation in 42.5%, and fibrosis in 25% of cases. Immunohistochemistry with melan A and/or HMB45 was studied for the detection of dermal invasion in 40%. Sentinel lymph node sampling was done in 2 patients with negative results. Invasive melanoma was detected in 22.5% of patients. Conclusion: Evaluation of regression in different types of MIS is valuable in the sense that upstaging can be conceivable in some clinical settings since it can be a sign of invasive melanoma. Step sectioning and immunohistochemical studies are important tools to detect invasion. Folliculotropism and vascular proliferation along with inflammation and melanophagocytosis are frequently seen in cases with regression. Regression in a dysplastic nevus is a known phenomenon and the severity of structural and cytologic atypia derive the diagnosis of MIS. OFP-07-010 Progressive disease in sentinel-negative melanoma patients: biological differences and importance of sentinel lymph node biopsy A. Conrad, U. Maccio*, M. Reinehr, D. Holzmann, J. Mangana, M. Wanner, M. Huellner, R. Barnhill, C. Lugassy, N. Lindenblatt, D. Mihic-Probst *University Hospital of Zurich, Switzerland Background & objectives: Among the most important prognostic factors in melanoma is the sentinel lymph node (SLN) status. Methods: Using our electronic database we identified 109 of 890 SLN-negative patients with progressive disease (PD). These patients were characterized for melanoma type, molecular type, sequence and extent of metastatic spread. Results: A total of 61 of 109 SLN-negative patients had PD in the SLN-basin indicating false-negative SLN (group-1). 48 of 109 patients had PD at distant sites and were therefore impossible to be identified using SLN biopsy (group-2). Despite distant spread these patients had significantly more single organ metastasis (p<0.001) and significantly longer disease-free-survival (p=0.001) compared to group-1. Additionally, to significant differences on a molecular basis between the two groups (p=0.01), all lentigo maligna and spindle-cell-melanomas belonged to group-2 and all, except one lentigo maligna melanoma, had single visceral metastasis. Conclusion: Two different biological groups among SLN-negative patients with PD were demonstrated. Extravascular-migratory- metastasis, rather than hematogenous spread, might be responsible for the observed PD with single organ involvement. OFP-07-011 PRAME expression in dysplastic nevi L. Innocenti*, R. Scarpitta, V. Ortenzi, A.G. Bonadio, B. Loggini, C. Scatena *University of Pisa, Italy Background & objectives: PRAME is a melanoma-associated antigen whose expression is well documented in cutaneous and ocular melanoma. Our study aimed to investigate the expression of PRAME in a series of low- and high-grade dysplastic nevi in which little is still known. Methods: Immunohistochemistry for PRAME was carried out on formalin-fixed paraffin-embedded samples applying the specific S30