Large-Scale EGFR Mutation Testing in Clinical Practice: Analysis of a Series of 18,920 Non-Small Cell Lung Cancer Cases

We make use of a very large dataset of non-small cell lung cancer specimens to examine the molecular epidemiology of EGFR mutations, particularly with respect to rare and compound mutations, and to non-adenocarcinoma histological subtypes. We also demonstrate the feasibility of large-scale EGFR mutation screening using the full range of specimens encountered in routine practice. We retrospectively reviewed 18,920 unselected EGFR mutation results from our centre between July 2009 and October 2016, using Qiagen's therascreen EGFR RGQ PCR Kit. Mutation rates were correlated with patient demographics and tumour histology. Our testing success rate was 93.9%, with similar success rates using histological and cytological specimens. Rare, potentially-targetable mutations accounted for 9.5% of all mutations detected. We identified a 2.5% mutation rate in tumours diagnosed as squamous cell carcinomas. There was a trend towards increasing EGFR mutation rates with increasing age, and while Del19 was the commonest mutation in the young, L858R predominated in the elderly. We found that EGFR mutation heterogeneity is rare within tumours and between primary and metastatic deposits. Our data demonstrate that large-scale, reflex EGFR mutation testing is feasible and affordable in the context of a publicly-funded health system. Furthermore, we have shown that the use of techniques sensitive only to classical mutations and selection of patients on the grounds of age, sex and histology denies patients access to potentially beneficial TKI therapy.