Abstract
Afatinib, a second-generation covalent EGFR TKI, has been approved for the treatment of the three "uncommon" EGFR mutations (G719X, S768I, and L861Q) based on one pooled retrospective analysis of three prospective trials (LUX-Lung 2, 3 and 6). The confirmed overall response rate, as assessed by independent radiology review, was 66% (95% confidence interval: 47-81). Among the 21 responders, the proportion of patients with response duration of ≥12 months was 52% and the proportion with response durations of ≥18 months was 33%. Of note, all patients received afatinib at 40 or 50 mg once daily which is higher than the approved dose of 40 mg once daily and the usual 30 mg once daily starting dose by most thoracic oncologists. Given the approval of afatinib for "uncommon" EGFR mutations was based on the limited number of patients analyzed, the retrospective nature of the analysis, lack of randomized phase 2 or 3 trial, there remains uncertainty as to whether afatinib, chemotherapy or other next-generation EGFR TKIs is the optimal treatment. This uncertainty also hinders the development of future treatment of these "uncommon" mutations because of the uncertainty that afatinib is the optimal treatment and hence should be the standard of care control arm in future randomized trials. Finally, the ACHILLES/TORG1834 provided us with the first randomized trial result that afatinib achieved superior progression-free survival over platinum-based chemotherapy (10.6 months vs 5.7 months, HR = 0.42; 95% CI: 0.256-0.694; P = 0.0007). However, ACHILLES should mostly be considered as phase 2 trial given the limited number (N = 109) of patients enrolled. Furthermore, the PFS benefit seemed to be with the 40 mg daily dose (HR = 0.128; 95% CI: 0.050-0.327) and not with the 30 mg daily dose (HR = 0.704; 95% CI: 0.352-1.406). Further investigation of the 30 once daily dosing for the treatment of uncommon EGFR mutations is needed.