ERBB3 and lung cancer: HER3 is a membrane enzyme encoded by the ERBB3 gene.127 Its most studied ligands are Neuregulin-1 and Neuregulin-2, which can bind to the extracellular domain of the receptor.127,128 Because HER3 lacks the kinase activating domain, its activity is carried out by heterodimerization with other HER-family receptors.129 HER3 overexpression is reported in various tumors, including breast and lung cancer, and correlates with poor prognosis.130-132 Patritumab deruxtecan (HER3-DXd) is the first-in-class HER3 targeting ADC, but other ADCs are under early development (eg, DR-1310).133,134