title: EGFR genetic heterogeneity of nonsmall cell lung cancers contributing to acquired gefitinib resistance.
abstract: Gefitinib is dramatically effective for nonsmall cell lung cancers (NSCLCs) with activating mutations of the epidermal growth factor receptor (EGFR) gene, but these tumors eventually develop drug resistance, attributable to a secondary T790M mutation or acquired MET amplification in some relapsed tumors. We analyzed EGFR mutations in matched pre- and post-therapeutic tumors of 6 gefitinib-responding lung cancers. With conventional PCR-based sequencing, classic mutations were detected in pretreatment samples of each case. The same mutations were readily confirmed in treated lesions of 4 cases, but were absent in those of Cases 1 and 2. Subsequent mutant-enriched peptide-nucleic-acid-mediated PCR clamping and subcloning assays detected the mutation in minor cells of treated lesions of Case 1, but still failed to detect a mutation in Case 2. We thus performed microdissection-based cell cluster mutation analysis of pretreatment tumors, and found that 3, including the first 2, concurrently contained tumor cells with either mutant or wild-type EGFR, although the latter was only a minor fraction. These findings suggest that some NSCLCs are genetically heterogeneous with regard to EGFR mutations; gefitinib-sensitive mutants decrease or vanish while wild clones selectively survive with gefitinib treatment. In addition, T790M was detected in a small fraction of treated lesions of 3 cases, and MET amplification was revealed in 3 treated tumors of Case 2. Thus, our results suggest that multiple mechanisms underlie acquired gefitinib resistance, and selection on a background of EGFR genetic heterogeneity also contributes to acquisition of resistance in a proportion of NSCLCs.
authors.affiliation: Department of Pathology, Kitasato University School of Medicine, Kanagawa, Japan. sxjiang@med.kitasato-u.ac.jp
authors.forename: Shi-Xu
authors.initials: SX
authors.lastname: Jiang
authors.forename: Kazuya
authors.initials: K
authors.lastname: Yamashita
authors.forename: Michiko
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Chun-Ji
authors.initials: CJ
authors.lastname: Piao
authors.forename: Atsuko
authors.initials: A
authors.lastname: Umezawa
authors.forename: Makoto
authors.initials: M
authors.lastname: Saegusa
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Yoshida
authors.forename: Masato
authors.initials: M
authors.lastname: Katagiri
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Masuda
authors.forename: Kazushige
authors.initials: K
authors.lastname: Hayakawa
authors.forename: Isao
authors.initials: I
authors.lastname: Okayasu
mesh_terms: D000368:Aged; D001483:Base Sequence; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D005091:Exons / Q000235:genetics; D005260:Female; D000077156:Gefitinib; D018740:Genetic Heterogeneity; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics; D011799:Quinazolines / Q000627:therapeutic use*
chemical_list: D011799:Quinazolines; D066246:ErbB Receptors; D000077156:Gefitinib