For example, in the Ku80+/− background, a high frequency of liver cancer was observed[40],whereas in p53 heterozygous and homozygous background, PARP-1 null mice developa variety of tumors, including mammary gland carcinoma, lung cancer, as well asbrain tumors (see [2, 41]). The gene discussed is XRCC5; the disease is liver cancer.