KRT18 and skin basal cell carcinoma: In seven-week-old Sprague-Dawley rats, e.g., spontaneous BCC tumors were observed as single, reddish-brown subcutaneous masses located at the left inguinal region, basaloid cells showed lobular and cribriform growth with high mitotic rates, and cytokeratin 14 and cytokeratin 18 were expressed in nest tumor cells, thereby indicating that spontaneous BCC can occur in young rats (Lee et al., 2010).