HER2-negative primary tumor samples found to have abnormal HER2-driven signaling by the CELx HSF test (n = 7) and HER2+ cell lines (n = 9) were further evaluated to determine the amount of signaling initiated by the NRG1b agonist that could be inhibited by a HER2 mAb (pertuzumab) and three small molecule pan-HER receptor tyrosine kinase (RTK) inhibitors (lapatinib, neratinib, and afatinib) at therapeutic concentrations (Fig. 4). Here, ERBB2 is linked to neoplasm.