Histological classification of cutaneous squamous cell carcinomas with different severity

Cutaneous squamous cell carcinoma (cSCC) is the second most common non-melanoma skin cancer. Histology represents the gold standard to confirm the diagnosis of cSCC and is mandatory to determine important findings for tumour grading, such as tumour thickness, depth of invasion, degree of differentiation and histological subtype, perineural and vascular invasion, and assessing tumour margins. In daily clinical practice, the combination of clinical and histological features should be considered when grading the tumours and treating the patients, accordingly. This article aims to provide a structured overview of the most common histological findings of in situ and invasive cSCCs, namely those relevant to their severity, and should facilitate the understanding and evaluation of these results.