Skin toxicity is a frequently observed side effect in the era of "molecularly targeted therapies". Skin toxicity following administration of protein kinase inhibitors such as sorafenib, regorafenib, lapatinib, sunitinib, and others can be debilitating to the patient, resulting in dose reduction and discontinuation of treatment. The mechanisms of skin toxicity induced by targeted chemotherapy, such as sorafenib or regorafenib, are poorly understood. Further research is warranted to better understand the pathophysiology of drug-related skin toxicity in this setting and develop correction strategies. This study tests the hypothesis that sorafenib and regorafenib interfere with p63 expression and keratinocyte differentiation and skin remodeling.