In contrast, mice that received Group 1 KP;RbTR/TR tumor spheroid lines but were treated with tamoxifen to reactivate RB were significantly less likely to have tumor masses overall (P = 0.015; Fig. 5A), and those animals which did have tumors had far fewer and smaller masses than their control counterparts (Fig. 5B–D). Here, RB1 is linked to neoplasm.