Somatic mutations in the tyrosine kinase domain of the epidermal growth factor 
receptor (EGFR) gene are present in lung adenocarcinomas that respond to the 
EGFR inhibitors gefitinib and erlotinib. Two types of mutations account for 
approximately 90% of mutated cases: short in-frame deletions in exon 19 and a 
specific point mutation in exon 21 at codon 858 (L858R). Screening for these 
mutations has been based mainly on direct sequencing. We report here the 
development and validation of polymerase chain reaction-based assays for these 
two predominant types of EGFR mutations. The assay for exon 19 mutations is 
based on length analysis of fluorescently labeled polymerase chain reaction 
products, and the assay for the exon 21 L858R mutation is based on a new Sau96I 
restriction site created by this mutation. Using serial dilutions of DNAs from 
lung cancer cell lines harboring either exon 19 or 21 mutations, we detected 
these mutations in the presence of up to approximately 90% normal DNA. In a test 
set of 39 lung cancer samples, direct sequencing detected mutations in 25 cases 
whereas our assays were positive in 29 cases, including 4 cases in which 
mutations were not apparent by sequencing. These assays offer higher sensitivity 
and ease of scoring and eliminate the need for sequencing, providing a robust 
and accessible approach to the rapid identification of most lung cancer patients 
likely to respond to EGFR inhibitors.