Purpose: In patients with non-small cell lung cancer (NSCLC), mutations in the epidermal growth factor receptor (EGFR) tyrosine kinase domain have been associated with sensitivity to erlotinib and gefitinib. We undertook this study to explore the relationship between EGFR mutation type and clinical variables, including treatment with gefitinib and erlotinib.Experimental Design: In patients with NSCLC, EGFR exon 19 deletion mutations and EGFR L858R point mutations were analyzed by nonsequencing PCR-based methods from paraffin blocks of tissue obtained before treatment. The results were correlated with clinical information (sex, pathologic subtype, race/ethnicity, treatment, and overall survival).Results: The two most common EGFR mutations were identified in 24% (70 of 291; 95% confidence interval, 26%-38%) of tumors from patients with NSCLC. EGFR mutation was associated with Asian ethnicity (P = 0.0023) and being a "never smoker" (P = 0.0001). Among patients with EGFR mutations, 39% (27 of 70) had EGFR L858R, whereas 61% (43 of 70) had an EGFR exon 19 deletion. After treatment with erlotinib (n = 12) or gefitinib (n = 22), patients with EGFR mutations had a median overall survival of 20 months. After treatment with erlotinib or gefitinib, patients with EGFR exon 19 deletions had significantly longer median survival than patients with EGFR L858R (34 versus 8 months; log-rank P = 0.01).Conclusions: EGFR mutations in exons 19 or 21 are correlated with clinical factors predictive of response to gefitinib and erlotinib. Those with EGFR exon 19 deletion mutations had a longer median survival than patients with EGFR L858R point mutation. These observations warrant confirmation in a prospective study and exploration of the biological mechanisms of the differences between the two major EGFR mutations.

7078 Background: We previously reported that in 2 of 5 non-small cell lung cancer (NSCLC) patients with acquired resistance to the tyrosine kinase inhibitors (TKIs), gefitinib and erlotinib, tumors biopsied after disease progression contained a second site mutation (T790M) in the epidermal growth factor receptor (EGFR) kinase domain, in addition to a primary drug-sensitive mutation (exon 19 deletion (del) or exon 21 point mutation (L858R)) (Pao et al, PLoS Med ‘05). No patients had KRAS mutations, which are associated with primary resistance to these TKIs. We sought to determine the frequency of second site EGFR kinase domain and KRAS mutations in tumors from patients with acquired resistance to TKIs, administered either as monotherapy or with chemotherapy. Methods: 18 patients with NSCLC who responded to either TKI alone (n = 14) or TKI plus chemotherapy (n = 4) and then progressed were re-biopsied. Genomic DNA samples from tumors were examined for EGFR (exons 18–24) and KRAS (exon 2) mutations. Results: Sequence analysis was successfully performed on tumors from 17 patients. The T790M EGFR mutation was detected in 6 of 13 (46%, 95% CI 19–75%) on TKI monotherapy, and in 0 of 4 (0%, 95% CI 0–53%) on TKI plus chemotherapy. In one autopsy case, the T790M mutation was detected in 5 of 5 sites, which all harbored the same exon 19 del. No other EGFR or KRAS mutations were detected. Conclusions: Secondary EGFR T790M but not KRAS mutations are commonly associated with acquired resistance to TKI monotherapy. More patients are being studied, and we are trying to elucidate determinants of acquired resistance in the absence of T790M mutations. New therapies are needed to treat and/or suppress the development of acquired resistance to gefitinib or erlotinib. Support: Joan’s Legacy, DDCF, K08-CA097980, R21-CA115051. [Table: see text]