A combination of three proteins comprising the receptors EGFR, ERBB3/HER3, and the cyclin-dependent kinase inhibitor p27 (CDKN1B) was found to be a potential biomarker for dependence on PI3K/AKT vs. MAPK/ERK signaling for drug resistance in HER2 breast cancers[52]. Here, ERBB2 is linked to breast cancer.