Tumorigenesis studies revealed that mammary tumor development was significantly accelerated in Neu/β2KO mice as determined by Kaplan-Meier analysis (median time for tumor onset 8 months for Neu/β2KO mice versus 11 months for Neu/β2WT mice, P < 0.0001) (Figure 5A). The gene discussed is ERBB2; the disease is breast cancer.