ERBB2 and breast neoplasm: Aside from the ErbB/HER pathway, HER2-positive breast tumors had frequent mutations in genes involved in receptor tyrosine kinase signaling (p < 0.001), homologous recombination (p < 0.001), checkpoint factors (p < 0.01), and p53 signaling and cell cycle (p < 0.01) as compared with HER2-zero (Fig. 3D) and HER2-low breast tumors (Fig. 3E).