To evaluate the correlation between the proliferative activity and the above-mentioned RB1CC1 pathway of RB1 activation involving p53 and hSNF5 in tumor tissue in vivo, we evaluated the expressional status of RB1CC1, RB1, p16, p21, Ki-67, p53 and hSNF5 in 59 cases of breast cancer. The gene discussed is RB1CC1; the disease is breast cancer.