Complex mutations in the epidermal growth factor receptor gene in non-small cell lung cancer

Mutation of the epidermal growth factor receptor (EGFR) gene can predict the efficacy of EGFR-tyrosine kinase inhibitors. Different mutations have been shown to co-occur in a single tumor. However, the frequency of these so-called "complex mutations" and the efficacy of gefitinib in treating patients with these mutations are unclear.

We investigated the frequency of complex mutations in 783 patients with non-small cell lung cancer seen at our institutes between April 2006 and May 2009. Mutational analysis was performed using the peptide nucleic acid-locked nucleic acid polymerase chain reaction clamp method. Gefitinib efficacy was evaluated in patients found to have complex mutations.

EGFR: mutations were detected in 318 (41%) patients, with 21 (6.6%) of these individuals having complex mutations. Sixteen of these 21 patients received gefitinib. The response rate (RR) was 67% (95% confidence interval [CI], 35-90%) and median progression-free survival was 12.2 months (95% CI, 1.3 months to undeterminable). Analysis of RR according to mutation type revealed that patients with deletional mutation in exon 19 (Del-19) and a point mutation in exon 21 (L858R) had a better RR (86%, 6 of 7) than those with other complex mutation patterns such as a point mutation in exon 18 (G719S) + L858R (40%, 2 of 5) (p = 0.2222). The median progression-free survival was also longer in these patients (16.5 months; 95% CI, 1.1 months to undeterminable versus 3.8 months; 95% CI, 0.7-10.0 months) (p = 0.0459).

Complex EGFR mutations are not rare. Gefitinib has different efficacy according to the type of complex EGFR mutations. Patients with Del-19 and L858R mutations may benefit more from gefitinib than other types of complex mutations.