Although all of the cell lines could form tumors at a density of 1 × 106 and 1 × 105 cells, CYP4Z1- or CYP4Z2P-3′UTR overexpressed cells showed increased tumor size and weight (Fig. 2a–d) while knockdown of CYP4Z1- or CYP4Z2P-3′UTR decreased the tumor-initiating ability of MCF-7 cells (Fig. 2a–f). The gene discussed is CYP4Z1; the disease is neoplasm.