ERBB2 and neoplasm: The study of spontaneous tumor development, progression, and metastasis in the context of an intact immune system is made possible by genetically engineered mice models (GEMM), such as Trp53 homozygous null, cMyc, Wnt1, PyMT, or Her2 overexpression models (Figure 4(Fig. 4)) (Lv et al., 2020[37]).