One set of mice were treated with tamoxifen, such that the knockout of Meis1 was induced one week before DMBA tumor initiation (referred to as “before-DMBA”) and the other set of mice were treated with tamoxifen, such that the knockout of Meis1 was induced nine weeks after DMBA tumor initiation (referred to as “after-DMBA”) (see Fig. 3A). The gene discussed is MEIS1; the disease is neoplasm.