Tissue heterogeneity of EGFR mutation in lung adenocarcinoma.

Tissue heterogeneity of EGFR gene mutation was studied in 10 formalin-fixed paraffin-embedded (FFPE) samples from four cases that demonstrated EGFR mutations in snap-frozen samples. EGFR mutations identical to those in frozen sample were demonstrated in 8 of 10 FFPE samples by direct sequencing and in 9 of 10 by fragment length analysis, but an exon-19 deletion mutation could not be identified in one FFPE sample analyzed by both techniques, despite multiple repeated assays. This suggests that some tumors may demonstrate intratumoral heterogeneity for the occurrence of EGFR mutation.