Diagnostic Accuracy of Ex Vivo Confocal Laser Scanning Microscopy for Routine Detection of Cutaneous Squamous Cell Carcinoma and Actinic Keratoses

Background and Objectives: Invasive cutaneous squamous cell carcinoma (cSCC) and actinic keratosis (AK) are growing burdens on ageing societies and mainly arise from chronic sun exposure. Distinguishing between carcinoma and carcinoma in situ is often clinically challenging but essential for decision-making with respect to targeted therapy. Ex vivo confocal laser scanning microscopy (CLSM) allows histologic examination of native tissue using tissue reflection and nuclear fluorescence staining. The digital staining process almost perfectly mimics conventional haematoxylin and eosin (HE) staining. While the use of CLSM for basal cell carcinoma (BCC) diagnosis is well described, data on cSCC remain scarce. The aim of this study was to compare CLSM with conventional histology in diagnosing and distinguishing cSCC and AK in routine clinical practice. Materials and Methods: Between August 2022 and March 2024, 63 patients with clinically suspected invasive cSCC or AK were enrolled. Biopsy or excision specimens were examined by ex vivo confocal laser scanning microscopy (VivaScope® 2500 M-G4) followed by acridine orange staining. All samples underwent subsequent routine histopathology, which served as the reference. Two dermatologists independently compared the CLSM findings with the histopathological diagnoses. Results: Eighty-one lesions suspected to be cSCC were assessed using CLSM. The diagnostic accuracy was high across specimen types: cSCC was correctly identified in 24/26 cases (92.3%), AK/Morbus Bowen in 16/17 cases (94.1%), cSCC filia (cutaneous squamous cell carcinoma metastases) in 3/3 cases (100%), and basal cell carcinoma in 9/9 cases (100%). The absence of a tumour was correctly recognized in 19/21 cases (90.5%). In five cases (6.2%), AK and early invasive cSCC could not be differentiated, reflecting the histopathological results. Conclusions: CLSM with digital HE staining is well suited for rapid cSCC and AK diagnosis and differentiation in clinical practice.