TBCE and squamous cell carcinoma: The keratin expression profile in PN epidermis was summarized (Table S3), they are different from the healthy epidermis, the psoriasis,30, 31 hypertrophic scar11 and squamous cell carcinoma,32 In a summary, hyperproliferative and aberrant differentiation of KCs are involved in the hard cornification in the thick epidermis development,6, 21, 33 it offers a deeper insight to understand epidermal hyperplasia and PN pathogenesis.