Search

Targeted cancer therapies impede cancer cell growth by inhibiting the function of activated oncogene products. Patients with non-small cell lung cancer and somatic mutations of EGFR can have a dramatic response to treatment with erlotinib and gefitinib; different somatic mutations are associated with different times to progression and survival. In this study, the relative and absolute potencies of two distinct EGFR tyrosine kinase inhibitors, erlotinib and an investigational irreversible inhibitor, HKI-272, were found to vary significantly in a panel of Ba/F3 cells transformed by representative EGFR somatic mutations. HKI-272 more potently inhibited the primary exon 20 insertion mutants, the secondary erlotinib-resistance mutants including T790M and many erlotinib-sensitive mutants including L858R. In contrast, erlotinib is a more potent inhibitor of the major exon 19 deletion mutants than is HKI-272. Analyses of EGFR autophosphorylation patterns confirmed the mutation-specific variation in relative potency of these tyrosine kinase inhibitors. Our finding that distinct EGFR inhibitors are more effective in vitro for different mutant forms of the protein suggests that tyrosine kinase inhibitor treatment could be tailored to specific EGFR mutations. More broadly, these results imply that the development and deployment of targeted therapies should focus on inhibition of specific cancer-causing mutations, not only on the mutated target.

As the literature about epidermal growth factor receptor (EGFR) mutations grows and screening for mutations becomes increasingly integrated into clinical care, it is important to examine how best to do somatic mutational analyses and how best to use the test results in clinical decision making. We began offering mutation screening by comprehensive direct sequence analysis of exons 18 to 24 of the tyrosine kinase domain of EGFR in August 2004 as part of clinical cancer care and protocol therapy at our institutions. All identified potential mutations are confirmed with three to five independent PCRs of the original genomic DNA sample and, if not previously noted in the literature, are compared with the patient's germ-line DNA to ensure the finding is somatic. We formally analyzed the first 100 patients to undergo EGFR sequence analysis and found that testing was feasible and significantly affected the treatment of patients with non-small cell lung cancer (NSCLC). Patients harboring EGFR mutations were significantly more likely to receive recommendations for therapy with EGFR tyrosine kinase inhibitors (i.e., gefitinib or erlotinib) than patients without mutations. However, negative EGFR test results did not prevent physicians from administering these agents to selected patients. Ideally, a standardized technique for mutation testing could be developed, with demonstrated reproducibility and validity. Clinical trials incorporating molecular diagnostics are ongoing to assess the efficacy of EGFR tyrosine kinase inhibitors as first-line therapy for metastatic NSCLC and as adjuvant therapy for early-stage resected NSCLC. It is likely that mutation testing and other molecular analyses will be most useful in these two clinical situations.

Purpose: Mutations in the epidermal growth factor receptor (EGFR) are associated with clinical and radiographic responses to EGFR tyrosine kinase inhibitors gefitinib and erlotinib. Currently available methods of EGFR mutation detection rely on direct DNA sequencing, which requires isolation of DNA from a relatively pure population of tumor cells, cannot be done on small diagnostic specimens, and lack sensitivity. Here we describe the use of a sensitive screening method that overcomes many of these limitations., Experimental Design: We screened 178 non-small cell lung cancer specimens for mutations in exons 18 to 21 of EGFR using a DNA endonuclease, SURVEYOR, which cleaves mismatched heteroduplexed DNA. Samples were analyzed by high-performance liquid chromatography on the Transgenomic WAVE HS system. Selected specimens that produced digestion products using SURVEYOR were subsequently reanalyzed by size separation or under partially denaturing conditions, followed by fractionation and sequencing. The specimens included DNA isolated from frozen tumor specimens, dissected formalin-fixed, paraffin-embedded tumor specimens undergoing clinical sequencing, and undissected formalin-fixed, paraffin-embedded specimens. One hundred sixty specimens were independently analyzed using direct DNA sequencing in a blinded fashion., Results: EGFR mutations were detected in 16 of 61 fresh frozen tumor specimens, 24 of 91 dissected formalin-fixed, paraffin-embedded tumor specimens, and 11 of 26 undissected formalin-fixed, paraffin-embedded tumor specimens. Compared with sequencing, the sensitivity and specificity of the present method were 100% and 87%. The positive and negative predictive values were 74% and 100%, respectively. SURVEYOR analysis detected 7 (4%) mutations that were not previously detected by direct sequencing., Conclusions: SURVEYOR analysis provides a rapid method for EGFR mutation screening with 100% sensitivity and negative predictive value. This unbiased scanning technique is superior to direct sequencing when used with undissected formalin-fixed, paraffin-embedded specimens.

Genome-wide copy number changes were analyzed in 70 primary human lung carcinoma specimens and 31 cell lines derived from human lung carcinomas, with high-density arrays representing approximately 115,000 single nucleotide polymorphism loci. In addition to previously characterized loci, two regions of homozygous deletion were found, one near the PTPRD locus on chromosome segment 9p23 in four samples representing both small cell lung carcinoma (SCLC) and non-small cell lung carcinoma (NSCLC) and the second on chromosome segment 3q25 in one sample each of NSCLC and SCLC. High-level amplifications were identified within chromosome segment 8q12-13 in two SCLC specimens, 12p11 in two NSCLC specimens and 22q11 in four NSCLC specimens. Systematic copy number analysis of tyrosine kinase genes identified high-level amplification of EGFR in three NSCLC specimens, FGFR1 in two specimens and ERBB2 and MET in one specimen each. EGFR amplification was shown to be independent of kinase domain mutational status.

Receptor tyrosine kinase genes were sequenced in non-small cell lung cancer (NSCLC) and matched normal tissue. Somatic mutations of the epidermal growth factor receptor gene EGFR were found in 15of 58 unselected tumors from Japan and 1 of 61 from the United States. Treatment with the EGFR kinase inhibitor gefitinib (Iressa) causes tumor regression in some patients with NSCLC, more frequently in Japan. EGFR mutations were found in additional lung cancer samples from U.S. patients who responded to gefitinib therapy and in a lung adenocarcinoma cell line that was hypersensitive to growth inhibition by gefitinib, but not in gefitinib-insensitive tumors or cell lines. These results suggest that EGFR mutations may predict sensitivity to gefitinib.