LAUSR

9036 Background: The nNGM centralizes molecular diagnostics, treatment recommendations and follow-up reporting in NSCLC in Germany. Uncommon EGFR mutations pose a clinical challenge because they comprise a heterogenous group and analyses of treatment outcome are still scarce. Here, we analyzed follow-up data of patients with rare EGFR mutations and performed functional characterization of recurrent mutations with unknown function. Methods: This multicenter, retrospective analysis of uncommon EGFR mutations (excluding L858R-, T790M mutations and exon 19 deletions) includes stage IV patients with NSCLC from 12 nNGM centers. We categorized EGFR-mutations into 3 groups: uncommon EGFR mutations with known driver function, for instance E709X, G719X, S768I and L861Q (group 1), exon 20 insertions (group 2) and all other very rare mutations (group 3). Functional characterization of unknown mutations was performed by insertion mutagenesis in Ba/F3 cells and monitoring of growth factor-independent proliferation. Results: In total, 834 cases with uncommon EGFR mutations were reported. Follow-up data after EGFR-TKI (Erlotinib, Gefitinib, Afatinib and Osimertinib), chemotherapy and/or mono-PD(L)1 blockade was available for 252 patients. Mean progression free survival (mPFS) on EGFR-TKIs vs. chemotherapy was 6.6 months vs. 5.0 months (HR 0.54, 95%CI 0.35 to 0.81, P =.003) in group 1 (n = 84), and 6.7 months vs. 3.4 months (HR 0.66, 95%CI 0.47 to 0.92, P =.015) in group 3 (n = 104). Mono-anti-PD(L1) blockade was not superior to chemotherapy (group 1, mPFS 3.0 months, HR 1.32, 95% 0.55 – 3.15, P =.535 and group3, mPFS 4.3 months, HR 1.02, 95% CI 0.64 – 1.62, P = 0.951). Exon 20 insertions (group 2, n = 63) did not benefit from EGFR-TKIs or anti-PD(L1) blockade vs. chemotherapy. Overall survival (OS) analysis (n = 218) following chemotherapy (56%) or EGFR-TKI treatment (44%) showed median OS (mOS) of 18.0 months vs. 13.9 months in patients treated with EGFR-TKI and chemotherapy, respectively in group 1 (HR 0.97, 95%CI 0.54 to 1.75, P =.929). In group 3 patients treated with EGFR-TKI and chemotherapy had a mOS of 35.4 months vs. 12.0 months, respectively (HR 0.59, 95%CI 0.35 to 1.01, P =.056). In the Ba/F3 system we could identify 8 recurrent driver and 12 non-driver mutations with a clinically applicable assay turnaround time of 4 weeks to inform clinical decision-making in the future. Conclusions: This real-world dataset confirms that patients with group 1(uncommon) EGFR mutations benefit from EGFR-TKIs and indicates that mono-anti PD(L)1 blockade is not superior to chemotherapy. Furthermore, patients with very rare EGFR mutations (group 3) also experienced a PFS benefit from EGFR-TKI compared to chemotherapy while immune therapy was not beneficial.