“ALKoma” in NSCLC- Optimizing Diagnosis and Treatment Strategies

Review Article

Austin J Cancer Clin Res. 2016; 3(2): 1071.

“ALKoma” in NSCLC- Optimizing Diagnosis and Treatment Strategies

Moskovitz M¹, Wolner M¹, Dudnik E³, Heshkovitz D4, Shlomi D5, Ilouze M3, Pekar-Zlotin M5 and Peled N2,3*

¹Department of Oncology, Rambam Health Care Campus, Israel

²Department of Medicine, Tel-Aviv University, Israel

³Department of Oncology, Davidoff Cancer Center, Israel

4Department of Pathology, Rambam Health Care Campus, Israel

5Thoracic Cancer Research and Detection Center, Sheba Medical Center, Israel

*Corresponding author: Nir Peled, Department of Oncology, Thoracic Cancer Service, Davidoff Cancer Center, Kaplan St, Petach Tiqva, 49100, Israel

Received: September 19, 2016; Accepted: November 30, 2016; Published: December 05, 2016


Lung cancer is the main cause of cancer-related death worldwide. In the last decade, certain molecular subgroups were identified, followed by development of different molecular-targeted treatments, which significantly improved the prognosis of these patients. Anaplastic lymphoma kinase echinoderm microtubule-associated protein-like 4 (ALK-EML4) rearrangements occur in 4-7% of patients with lung adenocarcinoma. ALK-EML4 tyrosine kinase inhibitors (TKIs) demonstrated significant clinical efficacy with higher overall response rate (ORR) and longer progression free survival (PFS) as compared with the traditional chemotherapy in the 1st and the 2nd line setting, although resistance development is inevitable and central nervous system (CNS) is a common site of failure. Numerous new agents are currently examined in clinical trials to overcome resistance to ALK inhibitors and improve the CNS penetrance and activity, and second line ALK-EML4 inhibitors are currently in clinical use. ALK-EML4 rearrangements are typically diagnosed by the FDA-approved Fluorescent In-Situ Hybridization (FISH) Break-Apart probe, however can also be detected by immunohistochemistry and next generation sequencing. This review will describe the current and future methods of ALK-EML4-rearrangement detection and treatment options for ALK-EML4-rearranged NSCLC.

Keywords: Lung cancer; Personalized therapy; ALK rearrangement; Crizotinib; Ceritinib


Molecular targeted therapy in NSCLC

Lung cancer is the main cause of cancer related death worldwide [1]. Over 70% of lung cancer patients are diagnosed with advanced disease, and receive palliative treatment with main purpose being life prolongation and symptoms management [2]. In the past, all Non-Small Cell Lung Cancer (NSCLC) patients were treated with chemotherapy regimens containing a platinum compound [3]. In the last decade, driver mutations in some of the lung carcinomas have been discovered; the most common drivers are mutations in theKirsten rat sarcoma (K-RAS) gene, Epidermal Growth Factor Receptor (EGFR) gene, and Anaplastic Lymphoma Kinase-rearrangements. These can be diagnosed in about 60% of lung adenocarcinoma patients, which allows for about 30% of patients to be treated with targeted therapy significantly prolonging their survival (median survival of 3.5 years) [4]. Additionally, these agents typically produce rapid and durable responses and have a favorable toxicity profile. However, acquired resistance inevitably develops. This review focuses on the main pitfalls in the diagnosis of ALK-EML4 rearrangements, clinical characteristics and available treatment options for ALK-EML4- rearranged NSCLC, as well as the acquired resistance mechanisms and overcoming strategies.

The anaplastic lymphoma kinase gene rearrangement

The ALK is a 200 kDa receptor tyrosine kinase, a member of the insulin receptor superfamily. The protein is encoded by the ALK gene located on chromosome 2p239, and has a large extracellular domain, a lipophilic transmembrane segment, and a cytoplasmic tyrosine kinase domain. Murine RNA blot hybridization analysis revealed expression of ALK in specific regions of the developing brain [5]. In humans, ALK protein is normally expressed in the small intestine, testis, and brain, but not in other tissues [6]. ALK is a dependent receptor, which has a pro-apoptotic activity in the absence of a ligand, and an anti-apoptotic activity in the presence of its ligand and when the kinase is intrinsically activated [7].The translocation involving the ALK gene was first described in 1994 in anaplastic large-cell non- Hodgkin’s lymphoma cells arising from activated T lymphocytes. This rearrangement fused the nucleophosmin (NPM) nucleolar phosphoprotein gene on chromosome 5q35 to ALK. About 60% of the lymphoma cells were associated with the translocation [6]. Mutations involving ALK as a suspected driver mutation was also found in familial and sporadic neuroblastoma, mainly by point mutations and gene amplification [8,9], and in inflammatory myofibroblastic tumors, mainly by gene rearrangement with Tropomyosin (TMP3 and TMP4) fusion oncoproteins [10].

In 2007 [11], Soda, et al. demonstrated that approximately 6% of NSCLC tumors carry a novel translocation in which the echinoderm microtubule-associated protein-like 4 (EML4) gene is fused to ALK, chromosomal translocation inv(2) (p21; p23). This translocation was proved to play a key role in the development of NSCLC, by the rapid growth of NSCLC lesions in transgenic mice that express EML4- ALK specifically in lung alveolar epithelial cells, and rapid response of these lesions to oral administration of small-molecule inhibitor of the kinase activity of ALK [11]. Another evidence to the driver role of ALK-EML4 rearrangement was found in a large-scale survey of tyrosine kinase activity in lung cancer [12]. Using a phosphoproteomic approach, Rikova, et al. [13] characterized phosphotyrosine signaling of 41 NSCLC cell lines and 150 NSCLC tumors, and identified a high level of ALK phosphorylation in several NSCLC tumor samples and in one cell line [13]. The ALK-EML-4 translocation caused ligandindependent dimerization of the receptor kinase domain, leading to uncontrolled proliferation and inhibition of apoptosis, although the exact pathways involved in the pathogenesis are yet to be determined [12]. Several other ALK fusion partners, including CLIP4-ALK and SOCS5-ALK have been identified later [14], while EML4 still represents the most common one.

Methods of detection of ALK-EML4 rearrangement

The guidelines for molecular testing recommend ALK-EML4 screening for every patient with adenocarcinoma of lung origin following a negative EGFR testing result [15]. Patients should not be excluded from testing on the basis of clinical characteristics. EGFR and ALK-EML4 testing is not recommended for lung cancer patients that lack any adenocarcinoma component, such as pure squamous cell carcinomas, pure small cell carcinomas, or large cell carcinomas lacking any immunohistochemistry (IHC) staining suggestive for adenocarcinoma differentiation.

Aiming to increase the pre-test probability, and based on the Israeli experience of ALK-EML4 testing in NSCLC patients, our group developed a predictive model. This model demonstrated that the ALK-EML4 fusion was significantly more prevalent in younger male patients (52.1 vs. 61.3 years, p=0.049), in whom every additional year reduced the chance to find the fusion by 7% [CI=0.93 (0.88 - 0.99), p=0.03] [16].

The ALK-EML4 rearrangement can be detected using several methods. The only FDA-approved method for patient selection for anALK-EML4 inhibitory therapy is Fluorescent In-situ Hybridization (FISH) Break-Apart probe. Other methodologies also include immunohistochemistry (IHC), RT-PCR and next generation sequencing (NGS) [17].

The FISH method allows direct visualization of the ALK-EML4 gene break apart. The dual color probes stain the DNA segments around the break apart site; therefore, a split signal indicates the presence of an ALK-EML4 rearrangement (Figure 1). This method is FDA-approved; although it is time consuming, expensive and not routinely available in all laboratories. Fur the more, Rodig, et al. revealed [18], that the probe does not identify all the positive cases, and the interpretation of the results can be especially difficult when the translocation is intra-chromosomal and the break apart pointes are close together [17,18]. In addition, it is not sensitive for intron abnormalities, which can only be detected by IHC and NGS [19]. Still, Crizotinib has been registered in the US, with the FISH test as an approved companion diagnostic test.