ERBB3 and cancer: As previously mentioned, the correlation between Her3 activation and the resistance to ER-, EGFR1 or Her2-directed therapies highlights the importance of simultaneously targeting the overexpressed receptor (e.g., EGFR1) that causes cancer development, and Her3, which is activated when the patients become resistant against the first treatment by increasing neuregulin (NRG) levels that result in Her3 expression.