Clinical features and outcome of patients with non-small-cell lung cancer who harbor EML4-ALK

Abstract

Purpose: The EML4-ALK fusion oncogene represents a novel molecular target in a small subset of non-small-cell lung cancers (NSCLC). To aid in identification and treatment of these patients, we examined the clinical characteristics and treatment outcomes of patients who had NSCLC with and without EML4-ALK.

Patients and methods: Patients with NSCLC were selected for genetic screening on the basis of two or more of the following characteristics: female sex, Asian ethnicity, never/light smoking history, and adenocarcinoma histology. EML4-ALK was identified by using fluorescent in situ hybridization for ALK rearrangements and was confirmed by immunohistochemistry for ALK expression. EGFR and KRAS mutations were determined by DNA sequencing.

Results: Of 141 tumors screened, 19 (13%) were EML4-ALK mutant, 31 (22%) were EGFR mutant, and 91 (65%) were wild type (WT/WT) for both ALK and EGFR. Compared with the EGFR mutant and WT/WT cohorts, patients with EML4-ALK mutant tumors were significantly younger (P < .001 and P = .005) and were more likely to be men (P = .036 and P = .039). Patients with EML4-ALK-positive tumors, like patients who harbored EGFR mutations, also were more likely to be never/light smokers compared with patients in the WT/WT cohort (P < .001). Eighteen of the 19 EML4-ALK tumors were adenocarcinomas, predominantly the signet ring cell subtype. Among patients with metastatic disease, EML4-ALK positivity was associated with resistance to EGFR tyrosine kinase inhibitors (TKIs). Patients in the EML4-ALK cohort and the WT/WT cohort showed similar response rates to platinum-based combination chemotherapy and no difference in overall survival.

Conclusion: EML4-ALK defines a molecular subset of NSCLC with distinct clinical characteristics. Patients who harbor this mutation do not benefit from EGFR TKIs and should be directed to trials of ALK-targeted agents.

Fig 1.

Diagnostic features of EML4-ALK–positive non–small-cell lung cancer (NSCLC). (A) Fuorescent in situ hybridization (FISH) reveals a split of red and green probes that flank the ALK translocation site in an EML4-ALK–positive tumor (arrows). (B) ALK immunohistochemistry reveals cytoplasmic ALK staining. (C) Hematoxylin and eosin staining of the same tumor. Arrows in (B) and (C) indicate signet ring cells, which are commonly found in EML4-ALK–positive tumors.

Fig 2.

Time to progression (TTP) and overall survival (OS) of EML4-ALK–positive patients compared with patients who have EGFR mutant and wild-type (WT)/WT tumors. (A) TTP on epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor monotherapy. (B) TTP on any first-line, platinum-based, combination regimen. (C) Kaplan-Meier survival plots of OS.

Fig A1.

Example of reverse transcriptase polymerase chain reaction (RT-PCR) detection of EML4-ALK in a primary tumor sample and cell lines (RT-PCR for GAPDH expression was also performed as a control for RNA extraction and cDNA synthesis). In this patient (PID5), (A) RT-PCR and (B) DNA sequencing demonstrate the presence of EML4-ALK variant 5 (Wong DW, et al: Cancer 115:1723-1733, 2009), in which exon18 of EML4 is fused to exon20 of ALK (lane 1). NCI-H2228 and NCI-H3122 have previously been shown to harbor EML4-ALK variants 3 and 1, respectively (Koivunen JP, et al: Clin Cancer Res 14:4275-4283, 2008). Variant 1, which results from a fusion of EML4 exon13 with exon20 of ALK, is also detected in this assay (lane 3), whereas variant 3, in which EML4 exon6 is fused to exon20 of ALK, is not (lane 2).