Patritumab Deruxtecan in Patients With Solid Tumor Harboring an NRG1 Fusion

The NRG1 gene is located on chromosome 8 (8p12 region) and encode NRG1. NRG1 gene is translated to generate six different proteins (I-VI) and at least 31 isoforms. NRG1 proteins are structurally related to EGF and contain an EGF-like motif that binds and activates ErbB3 and ErbB4. Upon ligand binding, these receptors form homodimers or heterodimers, which results in phosphorylation of the intrinsic kinase domain, and activation of the PI3K-AKT, MAPK, and other pathways. The overall incidence of NRG1 fusions is very rare. In many tumor types, only limited numbers of NRG1 fusion variant have been identified. By percentage, there is no organ dominance of the presence of NRG1 fusions. In an analysis of 21, 858 tumor specimens that underwent anchored multiplex PCR for targeted RNA sequencing, the prevalence of NRG1 fusions was 0.2%. Of these, CD74 was the most common partner (29%), followed by ATP1B1 (10%), SDC4 (7%), and RBPMS (5%), and most CD74-NRG1 fusions have been reported in patients with lung IMA. NRG1 fusions result in aberrant expression of the epidermal growth factor (EGF)-like domain of neuregulin-1 (NRG1) on the cell surface binds primarily to ErbB3 and ErbB4, leading to heterodimerization or oligomerization with other ERBB family members. NRG1-mediated activation of ErbB3 promotes dimerization with EGFR, ErbB2, and ErbB4. These partners phosphorylate ErbB3, forming docking sites for SH2-domain proteins, leading to pathologic activation of multiple signal transduction pathways, including the phosphoinositide 3-kinase (PI3K) pathway. Subsequently, ErbB3 expression was noted at high levels, and the proteins were phosphorylated, in fusion-positive cases. Targeting ErbB3 signaling therefore represents a promising therapeutic approach for patients with NRG1 fusion-positive malignancies.