Discovery of AMBRA1 and SQSTM1 (p62) as putative biomarkers to identify high risk subsets of patients with cutaneous squamous cell carcinoma.

e21541 Background: While surgical excision is largely curative, small subsets of patients with cSCC develop metastatic disease for which current AJCC/Brigham and Women’s Hospital staging criteria are unable to reliably identify. There is hence an unmet need for credible prognostic biomarkers to stratify patients based on personalised risk, guide the use of emerging therapeutic intervention for advanced disease and the rationalisation of current/future dermatological healthcare. AMBRA1 and SQSTM1 (p62) play a key role in autophagy and sustained keratinocyte differentiation; two vital processes disrupted in cSCC tumorigenesis, resulting in deregulated cell proliferation and autophagy-mediated tumour cell survival. While AMBRA1 expression is maintained in the normal epidermis its expression is lost in the tumour growth front of cSCCs. Conversely, p62 expression is maintained in basal keratinocytes within the normal epidermis but is lost in the peritumoural epidermis. Collectively these observations suggest tumoural AMBRA1 and peritumoural epidermal p62 expression as biomarkers of cSCC progression. The aim of the present study was to assess the immunohistochemical (IHC) expression of AMBRA1 and p62 in a retrospective cohort of localised or metastatic cSCCs and correlate expression with clinical outcome over 5 years. Methods: Automated IHC analysis of AMBRA1 and p62 expression was performed in a retrospective cohort of well, moderately or poorly differentiated non or metastatic cSCCs. Digital images were annotated prior to H-score expression analysis using optimised cytoplasmic algorithms within Aperio ImageScope software. Results: Receiving Operating Characteristic (ROC) curve analysis revealed an H score of < 20 for peritumoural epidermal p62 and < 60 for expression of AMBRA1 in the cSCC growth front defined cSCCs at high risk of progression while tumours with a p62 H score of ≥ 20 and/or ≥ 60 for AMBRA1 were defined as low risk. Subsequent Kaplan Meier analysis of 51 moderately/poorly differentiated cSCCs demonstrated loss of peritumoural p62 and tumour AMBRA1 expression in 7 tumours correlated with a significantly increased risk of metastasis of 85.7 % compared to 25% for 44 tumours defined as low risk (P < 0.0001, HR 30.07, 95% CI 5.48-165) with an assay specificity of 97%, positive predictive value of 75%, and a negative predictive value of 86%. Conclusions: Overall these data suggest the combined use of tumoural AMBRA1 and peritumoural p62 expression as a putative prognostic biomarker for cSCC metastasis, the future validation of which may provide a valuable stratification tool to guide clinical management, therapeutic intervention and the rationalisation of healthcare resources.