Abstract 2221: Molecular analysis finds excision margin width predictive of recurrence in acral melanoma

Abstract Surgical excision with histologically clear margins results in cure of most melanoma patients. Involvement of the margins is associated with tumour recurrence and adverse outcomes. Determining whether or not the histological margins are involved by melanoma, particularly in situ melanoma, can be very difficult particularly in acral locations where insitu melanoma can be extremely subtle. This study sought to determine the proximity of acral melanoma in situ to the surgical excision margin using multiple methods including routine histopathological assessment, FISH (CCND1 amplification), and multiplex immunofluorescence (mIF: SOX10, p16, Cyclin D1 and PRAME) in primary acral melanomas with initially histopathologically reported clear excision margins of >0.3mm (n=85). The clear excision margins determined by each modality were compared between those melanomas which recurred (n=47) and those which remained recurrence-free at last follow-up (median = 46 months, range = 1-260 months) (n=35). Histopathologically confirmed excision margin width was smaller in the tumours of patients who recurred (mean = 7.083mm vs 9.964mm, p = 0.0811). Intratumoural CCND1 amplification was increased in recurrence-free patients in comparison to recurrence patients (16.2% vs 7.7%). FISH and mIF confirmed the correlation of intratumoural CCND1 amplification with Cyclin D1 expression SOX10+ melanoma cells (p=0.0347). No correlations between recurrence status and Cyclin D1, PRAME or p16 expression levels in the tumour or epidermis were identified. In histopathologically normal epidermal tissue as assessed on H&E sections,Cyclin D1+, p16- and PRAME+ cells were classified as malignant cells when co-expressed with SOX10. Upon measuring the distance from the tumour margin to the nearest malignant cell, we found that malignant cells were closer to the tumour in recurrence patients in comparison to recurrence-free patients (mean = 7.324mm vs 9.464mm, p = 0.2735). These distances closely correlated with the excision margin width as determined via histopathological assessment (R2 = 0.7424, p<0.0001). In conclusion, histological assessment, FISH and mIF determined excision margins are highly correlative in acral melanomas. Narrower excision margins were associated with local recurrence of melanoma. Citation Format: Grace Heloise Attrill, Teresa A. Bailey, Trina Lum, Jordan W. Conway, Georgina V. Long, James S. Wilmott, Richard A. Scolyer. Molecular analysis finds excision margin width predictive of recurrence in acral melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2221.