EGFR High Copy Number Together With High EGFR Protein Expression Predicts Improved Outcome for Cetuximab-based Therapy in Squamous Cell Lung Cancer: Analysis From SWOG S0819, a Phase III Trial of Chemotherapy With or Without Cetuximab in Advanced NSCLC

Background: The phase III S0819 trial investigated addition of cetuximab to first-line chemotherapy (CT) in NSCLC. Subgroup analyses suggested an OS benefit among patients with EGFR copy number gain in squamous cell carcinomas (SCC), (HR = 0.58 [0.39-0.86], P = .0071). A more detailed model based on EGFR FISH, EGFR IHC and KRAS mutation status was evaluated to yield a more precise predictive paradigm of cetuximab-based therapy in advanced NSCLC. Methods: FISH was performed using the Colorado Scoring Criteria; H-Score was used to quantify EGFR IHC expression (cut-off ≥ 200). A Cox model was used to assess treatment effects for OS and PFS within biomarker and clinical subgroups. KRAS mutation was analyzed using Therascreen. The false discovery rate controlled for multiple comparisons. S0819 ClinicalTrials.gov Identifier: NCT00946712. Results: Of 1,313 eligible patients, assay results were obtained for FISH on 976 patients (41% positive), for IHC on 945 patients (31% positive), and KRAS mutation status on 627 patients (26% positive). In SCC patients, OS was significantly improved with addition of cetuximab when both EGFR FISH and EGFR IHC were positive (N = 58), (OS HR: 0.32 [95% CI 0.18-0.59]; P = .0002, q = 0.08), median 12.6 versus 4.6 months. The results were independent of KRAS mutation status. In Non-SCC, no predictive value of EGFR IHC, EGFR FISH status and/or KRAS status was seen. Conclusions: In NSCLC SCC, a combination index of EGFR FISH plus EGFR IHC results was associated with improved OS when cetuximab was added to CT, representing a potential predictive molecular paradigm for patients suitable for EGFR-antibody therapy.