CLDN3 and skin squamous cell carcinoma: In our series, claudin-3 expression was mostly diffuse in normal skin (80% of the cases) and its immunostaining progressively decreased from flat wart (diffuse expression in 56% of the cases), to in situ cSCC (focal expression in 63% of the cases) and finally to invasive cSCC, which showed no claudin-3 expression in 52% of the cases.