Epidermal growth factor receptor (EGFR) gene amplification in non-small cell lung cancer (NSCLC): molecular patterns and sensitivity to tyrosine kinase inhibitors: A5-01

Gene amplification is a cellular process characterized by selective increase in the copy numbers of a DNA segment including one or more genes. The phenomenon amplifies the phenotype conferred by these genes and is known to be a major source for overexpression of oncogenes in cancer. In addition, amplified and overexpressed genes have been targeted in developmental therapeutic approaches, improving survival and reducing side effects of treatment. In NSCLC, EGFR is an example of these two situations: gene amplification associates with protein overexpression and anti-EGFR approaches have been developed as antibodies and small molecules (TKI) that inhibit the tyrosine kinase domain of the gene. This study investigated the patterns of EGFR gene amplification detected in NSCLC and their association with sensitivity to TKIs. Dual-color FISH assays with LSI SO EGFR/SG CEP 7 (Vysis/Abbott Molecular) were performed in tumors from 1225 NSCLC patients treated with gefitinib or erlotinib. EGFR gene amplification was detected in 102 specimens (8.3%) and molecular patterns were recognized. Outcome to treatment included response according to RECIST criteria, time to progression and overall survival. Amplified genomic segments were manifested as two recognizable forms: homogeneously staining regions (HSR), which are repeated genomic regions located intra-chromosomally, were found in 100 (98%) tumors; and double minute chromosomes (DM), which are extra-chromosomal segments of amplified DNA, were found. in two cases. Among the HSC cases, 47 tumors had a large number of EGFR copies per cluster (10 to >50) while 25 had a smaller number (4 to >10 copies per cluster). In all these cases the signals were loosely arranged. In 12 tumors, the clusters comprised very tightly arranged signals, making the enumeration practically impossible. In 9 tumors, the EGFR signals had an abnormally large and bright presentation although multiple spots were not visible. Another clustered pattern consisted of co-localization of EGFR and CEP 7 signals, in which the number of repeats were high (4 tumors) or low (3 tumors). In these cases, sequences of CEP 7 were either included in the amplicon or interspaced with EGFR sequences. The distribution of EGFR-amplified cells in the tumor section was restricted to some foci in 18% of cases, and was diffusely spread throughout the entire specimen in 82% of cases. Patterns of EGFR gene amplification in NSCLC are complex and heterogeneous. Accurate laboratorial diagnosis is critical for applicability of this phenomenon as a marker to select patients for therapy with EGFR TKIs. Correlation of the distinct patterns of EGFR gene amplification with sensitivity to TKIs is ongoing and will be presented at the meeting.