In addition, immunohistochemistry using keratin 1 (K1, an epithelial cell marker that is lost upon cancer progression22) antibodies confirmed the low expression of K1 in tumor samples from both Nf1f/f (Fig. 1f) and K14Cre; Nf1f/f (Fig. 1g) mice, although K1 is highly expressed in normal margin epidermis (Fig. 1h, i). This evidence concerns the gene KRT1 and neoplasm.