ErbB2 activation is dependent on ErbB2 homodimers or heterodimers with other ErbB family members (ErbB1, 3, 4), which could stimulate constitutive phosphorylation of ErbB2 and initiate the main downstream PI3K/AKT pathway and MAPK pathway, culminating in tumor growth. The gene discussed is EGFR; the disease is neoplasm.