Quantitative Protein Expression of Antibody–Drug Conjugate Targets in EGFR Mutated and Wild-type Non–Small Cell Lung Cancer

PURPOSE: Antibody-drug conjugates (ADC) are a promising approach for the management of patients with non-small cell lung cancer (NSCLC). However, only a small subset of patients derive benefit from these therapies. EXPERIMENTAL DESIGN: We used quantitative immunofluorescence assays to measure the levels of four ADC target proteins (HER2, TROP2, HER3, and EGFR) in three NSCLC tissue microarray cohorts stratified according to EGFR mutation [EGFR mutated (n = 83), EGFR wild-type (n = 128), and EGFR unknown (n = 232)]. Assay limits were established by mass spectrometry on standard cell lines. RESULTS: All four targets demonstrated a broad and comparable dynamic range of expression in all three cohorts. High proportions of cases were above the assay limits for all targets. A comparison of target expression showed a significant association of HER2 with EGFR expression and a nonsignificant association with EGFR mutation (P = 0.0005 and 0.14, respectively). TROP2 expression was not associated with EGFR expression or mutation. HER3 demonstrated a significant negative correlation with EGFR mutation but no significant association with EGFR expression (P < 0.0001 and 0.9869, respectively). EGFR expression was significantly associated with EGFR mutation (P = 0.047). CONCLUSIONS: ADC targets are highly expressed in NSCLC, implying that the benefit from these agents may be broad. Benefit from these therapies may go beyond mutation status, and fully quantitative approaches may help select patients for ADC targeting. Intertarget correlation may provide an insight on the underlying signaling pathways and/or treatment-related resistant mechanisms. In the future, quantitative immunofluorescence may be a valuable tool to select ADC treatment sequence. See related commentary by Hirsch, p. 2550.