Basal cell carcinoma of the skin (BCC) is the most common cancer in humans and its major risk factor is UV light exposure. Great advances in the understanding of the genetics of this cancer have arisen in recent years. It's now known that the aberrant activation of the hedgehog signaling pathway is important in the carcinogenesis of sporadic basal cell carcinoma. Also, the tumor suppressor gene TP53 is known to be highly mutated in BCCs. BCCs show an atypical growth pattern as it's a slowly growing tumor, rarely metastasizes and is rarely lethal. Incidence of BCCs increase with UV light exposure and age, that's why it's common that patients develop several tumors at the same time or throughout their life. During this study, high quality exome and cancer panel sequencing data were used in an attempt to define the clonality of BCC's tumors in 25 patients with multiple BCCs' tumors.