A recurrent gene fusion between EML4 and ALK in 6.7% of non-small cell lung cancers (NSCLCs) and NKX2-1 (TTF1, TITF1) high-level amplifications in 12% of adenocarcinomas of the lung were independently reported recently.
EML4-ALK was investigated in 266 resected primary NSCLC, including adenocarcinomas (AD), lymphoepithelioma-like carcinomas, squamous cell carcinomas, mucoepidermoid carcinomas, and adenosquamous carcinomas, by reverse transcriptase-polymerase chain reaction and was verified by sequencing.
Although ALK gene rearrangements affect only about 4% of all lung cancers, they are more frequent in adenocarcinomas, in never or light smokers, and seem almost mutually exclusive with activating EGFR or KRAS mutations.
Target therapies against echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase fusion protein or a mutated ERBB2 (v-ERB-B avian erythroblastic leukemia viral oncogene homologue 2) present in approximately 5% and approximately 3% of the Japanese patients with adenocarcinomas, respectively, are currently under development.
Primary SRC of the lung is a rare subtype of adenocarcinoma, carries a worse prognosis when compared to adenocarcinoma and shares many of the recently identified clinicopathologic characteristics ascribed to EML4-ALK positive non-small cell lung cancer.
The clinicopathological features of EML4-ALK-positive adenocarcinoma are reported to include its high incidence in young, non-smoking patients, tumors that show distinct solid or acinar growth patterns with or without signet-ring cell histology, and its mutually exclusive occurrence with mutations in EGFR and KRAS.
Patients with ALK rearrangements tended to be younger than those without the rearrangements, and most of the patients had little or no exposure to tobacco and had adenocarcinomas.
With the emergence of selective kinase inhibitors targeting epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK), there is a corresponding need to identify the subset of NSCLCs harbouring specific genetic mutations associated with sensitivity to these agents, almost all of which are found in adenocarcinomas.
NSCLC with the EML4 (echinoderm microtubule-associated protein-like 4)-ALK (anaplastic lymphoma kinase) fusion gene is also more likely to occur in never smokers and in those with adenocarcinoma histology, and is expected to benefit from ALK inhibitors.
ALK gene rearrangement occurs in approximately 3-5% of non-small-cell lung cancer patients, most of whom are never- or light smokers and have adenocarcinoma histology.
ALK mutations have been identified in approximately 2.4-13% of patients with NSCLC, occurring more frequently in adenocarcinomas and never and light smokers.
2 excision lung biopsy cases with pure (100%) signet-ring morphology and solid patterns demonstrated diffuse moderate cytoplasmic ALK immunoreactivity (2+) and harboured ALK rearrangements (p=0.007), unlike 5 mixed-signet-ring and 11 non-signet-ring adenocarcinomas, which showed negative or 1+ immunoreactivity; and did not harbour ALK rearrangements (p>0.1).
In 2011, the French National Cancer Institute recommended ALK-fluorescence in situ hybridization (FISH) testing in all EGFR/KRAS-negative adenocarcinomas by all the hospital molecular genetics platforms of cancers; however, this technique remains time and cost consuming and not suitable for a large-scale screening, in contrast to immunohistochemistry (IHC).
ALK rearrangement was significantly higher in adenocarcinomas (6.8%, p<0.001), younger age (p<0.0007), women (7.6%, p<0.001), and never-smokers (8.9%, p<0.001) with no gender difference in the adenocarcinoma or never-smoker subgroup.