Epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) are standard therapy for EGFR-mutant non-small cell lung cancer (NSCLC). Preclinically, HER3 ligand heregulin induces resistance to EGFR-TKIs, whereas the pan-human EGFR family inhibitor afatinib remains effective. Here, we examined whether soluble heregulin levels have clinical implications for EGFR-mutant NSCLC treated with EGFR-TKIs. Soluble heregulin was immunologically measured in plasma from EGFR-mutant NSCLC patients. Cutoff values were determined by 1-year PFS ROC curve. The relationship between soluble heregulin and PFS following EGFR-TKI therapy was analyzed by Cox proportional hazards model. Seventy-three patients were enrolled: 44 were treated with 1st-generation and 29 with 2nd-generation EGFR-TKIs. Soluble heregulin levels varied (range: 274–7,138 pg/mL, median: 739 pg/mL). Among patients treated with 1st-generation EGFR-TKIs, those with high heregulin (n = 20, >800 pg/mL) had a tendency for shorter PFS than those with low heregulin (n = 24, <800 pg/mL), with median PFS of 322 and 671 days, respectively. Cox proportional hazards model also indicated a trend toward resistance against 1st-generation EGFR-TKIs (HR: 1.825, 95% CI: 0.865–4.318) but not against 2nd-generation EGFR-TKIs. Soluble heregulin potentially correlates with resistance to EGFR-TKIs but not 2nd-generation EGFR-TKIs in patients with EGFR-mutant NSCLC.
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