KRT15 and basal cell carcinoma: In addition to the long debate on the origin of tumours that are derived from the skin appendages of basal cell carcinoma, the most frequent one, in particular, we have previously reported that Lgr5, Lrig1, and cytokeratin 15 were expressed in all skin appendage tumours tested, and expression of Lgr5 and Lrig1 was generally lower expressed in more aggressive tumour types such as sclerosing basal cell carcinoma and late porocarcinoma stage than in less aggressive superficial or nodular basal cell carcinoma or early porocarcinoma and sebaceous gland tumours [24].