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Disclosures: Alice T Shaw, MD, PhD Consultant/Advisory Boards: Pfizer [ALK inhibitors (Crizotinib)]; Novartis [ALK inhibitors (Ceritinib)]; Ariad [ALK inhibitors (AP26113)]; Genentech [ALK inhibitors (Alectinib)]; Ignyta [ALK inhibitors (RXDX101)]. Benjamin Solomon, MBBS, PhD Constultant/Adivsory Boards: Pfizer [cancer-NSCLS (Crizotinib)]; Novartis [cancer-NSCLC (LDK378 (ceretinib))]. James R Jett, MD Grant/Research/Clinical Trial Support: Oncimmune [lung cancer biomarkers (early CDT lung blood test)]; Metabolomx [biomarker lung cancer (breath and urine test in development)]. Consultant/Advisory Boards: Quest Diagnostics [lung cancer biomarkers (blood test in development)]. Rogerio C Lilenbaum, MD, FACP Consultant/Advisory Boards: Genentech [Lung Cancer (Bevacizumab)]; Boehringer-Ingelheim [Lung Cancer (Afatinib)]. Michael E Ross, MD Employee of UpToDate, Inc.

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Literature review current through: Nov 2014. | This topic last updated: Oct 14, 2014.

INTRODUCTION — A group of patients with non-small cell lung cancer (NSCLC) have tumors that contain an inversion in chromosome 2 that juxtaposes the 5' end of the echinoderm microtubule-associated protein-like 4 (EML4) gene with the 3' end of the anaplastic lymphoma kinase (ALK) gene, resulting in the novel fusion oncogene EML4-ALK [1]. This fusion oncogene rearrangement is transforming both in vitro and in vivo and defines a distinct clinicopathologic subset of NSCLC.

Tumors that contain the EML4-ALK fusion oncogene or its variants are associated with specific clinical features, including never or light smoking history, younger age, and adenocarcinoma with signet ring or acinar histology. ALK gene arrangements are largely mutually exclusive with epidermal growth factor receptor (EGFR) or KRAS mutations [2]. Screening for this fusion gene in NSCLC is important, as "ALK-positive" tumors (tumors harboring a rearranged ALK gene/fusion protein) are highly sensitive to therapy with ALK-targeted inhibitors.

The molecular pathogenesis, clinical features, and treatment of NSCLC associated with the ALK fusion oncogene are discussed here.

An overview of the treatment of metastatic NSCLC is presented separately, as are the indications for molecular testing. (See "Overview of the treatment of advanced non-small cell lung cancer" and "Personalized, genotype-directed therapy for advanced non-small cell lung cancer", section on 'Molecular testing'.)

MOLECULAR PATHOGENESIS — The echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK) fusion oncogene arises from an inversion on the short arm of chromosome 2 (Inv(2)(p21p23)) that joins exons 1-13 of EML4 to exons 20-29 of ALK [3]. The resulting chimeric protein, EML4-ALK, contains an N-terminus derived from EML4 and a C-terminus containing the entire intracellular tyrosine kinase domain of ALK.

Since the discovery of this fusion oncogene in 2007, multiple variants of EML4-ALK have been reported, all of which encode the same cytoplasmic portion of ALK but contain different truncations of EML4 (figure 1) [3-5]. In addition, fusions of ALK with other partners including TRK-fused gene TFG and KIF5B have also been described in lung cancer patients, but appear to be much less common than EML4-ALK [5,6].

For EML4-ALK, the EML4 fusion partner mediates ligand-independent dimerization and/or oligomerization of ALK, resulting in constitutive kinase activity. In cell culture systems, EML4-ALK possesses potent oncogenic activity [3]. In transgenic mouse models, lung-specific expression of EML4-ALK leads to the development of numerous lung adenocarcinomas [7].

The oncogenic role of the ALK fusion oncogene provides a potential avenue for therapeutic intervention. Cancer cell lines harboring the EML4-ALK translocation are effectively inhibited by small molecule inhibitors that target the ALK tyrosine kinase (TK) [8]. In vivo, treatment of EML4-ALK transgenic mice with ALK inhibitors results in tumor regression [7], supporting the notion that ALK-driven lung cancers are "addicted" to the fusion oncogene.

DIAGNOSIS — Anaplastic lymphoma kinase (ALK) gene rearrangements or the resulting fusion proteins may be detected in tumor specimens using fluorescence in situ hybridization (FISH), immunohistochemistry (IHC), and reverse transcription polymerase chain reaction of cDNA (RT-PCR) [9].

FISH – The gold standard assay for diagnosing ALK-positive NSCLC is FISH [10-13]. The commercial break-apart probes include two differently colored (red and green) probes that flank the highly conserved translocation breakpoint within ALK. In non-rearranged cells, the overlying red and green probes result in a yellow (fused) signal; in the setting of an ALK rearrangement, these probes are separated, and splitting of the red and green signals is observed (picture 1A-B). Atypical patterns of rearrangement have also been identified, and these are also responsive to ALK inhibition. ALK gene amplification alone is not predictive of responsiveness to these agents and does not carry the same significance as rearrangement.

IHC – Multiple monoclonal antibodies have been developed to use for the IHC detection of the ALK fusion oncogene, and IHC using these antibodies is highly sensitive and specific [14]. Thus, IHC can potentially be used to screen for and identify the presence of ALK positivity. In the United States, FISH is the only approved test to diagnose ALK-positive NSCLC, and thus FISH should be used to confirm the IHC results. In Europe, immunohistochemistry is widely used to detect ALK rearrangement.

RT-PCR – RT-PCR of cDNA has been a commonly used screening strategy for detecting ALK gene rearrangements in NSCLC, but is no longer recommended [15]. A number of multiplex assays were developed to simultaneously capture all possible in-frame fusions between EML4 and ALK in which the kinase domain of ALK would be preserved [3,8,16]. While different breakpoints in EML4 or ALK may be detected, novel ALK fusion partners will not. Furthermore, this method is frequently limited by the quality of the RNA that can be isolated from archival tissue.

CLINICOPATHOLOGIC FEATURES — With increasing identification of this molecular abnormality, the key epidemiologic, demographic, and pathologic features associated with anaplastic lymphoma kinase (ALK) fusion oncogenes have been identified.

Epidemiology — In unselected NSCLC populations, the ALK rearrangement is a relatively rare event. In the initial report, 5 of 75 lung tumors (7 percent) demonstrated expression of the fusion transcript. The overall incidence of ALK gene rearrangements in subsequent series has been about 4 percent [3,8,11-13,16-18]. Except in rare cases, the presence of ALK gene rearrangements in NSCLC tumors tends to occur independent of epidermal growth factor receptor (EGFR) or KRAS mutations. Similar frequencies of ALK gene rearrangements have been reported in Asian and Western populations [19].

While the overall frequency of ALK fusion oncogene in the general NSCLC population is low, knowledge of the clinicopathologic features enables enrichment for this genetically defined subset. In one study in which patients were selected for genetic screening based on clinical features commonly associated with EGFR mutation, including never/light smoking status and adenocarcinoma histology, 13 percent harbored the ALK fusion oncogene. Within the group of never or light smokers in this study, the frequency of ALK positivity was 22 percent, and among never or light smokers who did not have an EGFR mutation, the frequency was 33 percent [12]. These findings suggest that in NSCLC patients with clinical characteristics associated with EGFR mutation but with negative EGFR testing, as many as one in three may harbor the ALK fusion oncogene. (See "Systemic therapy for advanced non-small cell lung cancer with an activating mutation in the epidermal growth factor receptor", section on 'Rationale'.)

Age of onset — Patients with ALK fusion oncogene-positive lung cancer are relatively younger at onset than those without this abnormality [12,20]. The two studies that were used to support the approval of crizotinib included 255 patients whose tumors contained an ALK fusion oncogene; in this database, the median age was 52 years (range 21 to 82 years) [20]. The estimated median age for unselected patients with lung cancer is approximately 70 years [21].

Interestingly, other cancers known to harbor ALK rearrangements such as NPM-ALK positive anaplastic large cell lymphoma are also associated with younger age and are, in fact, most common in children and young adults.

Smoking history — The ALK fusion oncogene in patients with NSCLC is strongly associated with a history of never or light smoking (<10 packet years) [1,12,20]. In the crizotinib study database of 255 patients, never smokers and former smokers comprised 70 and 28 percent of cases, respectively [1,12,20].

Histology — The vast majority of lung tumors that harbor the ALK fusion oncogene are adenocarcinomas. In the 255 patients with the ALK fusion oncogene included in the crizotinib database, 97 percent were adenocarcinoma [20]. ALK rearrangement has been reported in squamous cell carcinoma, but this is rare [11,18].

Adenocarcinomas in ALK fusion oncogene positive cases from Caucasian patients are significantly more likely to have abundant signet ring cells than those with an EGFR mutation or wild type tumors [22]. Signet ring cells are frequently found in gastric cancers and rarely in cancers of other organs such as the lung. Several small case series suggest that signet ring cells may be associated with an aggressive clinical course and a poor prognosis. Whether the presence of signet ring cells in ALK fusion oncogene lung cancer has biological or clinical significance remains to be determined.

Other studies of ALK in NSCLC have not reported an association with signet ring cells, but have noted a possible association with the acinar subtype of adenocarcinoma, at least in Asian patients. This discrepancy may reflect differences in pathologic interpretation rather than ethnic differences in patients with ALK fusion oncogene-positive lung cancer.

CHEMOTHERAPY VERSUS TARGETED THERAPY — Advanced non-small cell lung cancer (NSCLC) associated with the anaplastic lymphoma kinase (ALK) fusion oncogene is highly sensitive to ALK tyrosine kinase (TK) inhibitors. Treatment with ALK TK inhibitors should be limited to patients whose tumors contain this abnormality as demonstrated by fluorescence in situ hybridization (FISH). (See 'Diagnosis' above and "Overview of the treatment of advanced non-small cell lung cancer", section on 'Initial systemic therapy'.)

An ALK inhibitor is preferred as the initial therapy for patients whose tumor contains this genetic abnormality in countries where it is approved for this indication. Preliminary results of a phase III trial comparing ALK inhibition using crizotinib with chemotherapy in treatment naïve patients have demonstrated a prolongation in progression-free survival, but not overall survival [23]. (See 'Crizotinib' below.)

In other countries, its use may be restricted to those who have progressed following chemotherapy. Thus patients should have tumor tissue assessed for the presence of ALK rearrangement, as well as for other driver mutations (especially in the epidermal growth factor receptor [EGFR]). (See "Personalized, genotype-directed therapy for advanced non-small cell lung cancer", section on 'Molecular testing'.)

If systemic treatment is required before the results of genotype testing are available, systemic chemotherapy rather than targeted therapy is indicated [24]. When the results of genotype testing become available, the treatment plan should be reassessed. There are no clinical trials that directly address the optimal timing of ALK inhibitors in patients who have already started on chemotherapy (algorithm 1).

If an ALK fusion oncogene is identified after the initiation of treatment, we suggest continuing chemotherapy for four cycles if therapy is tolerated and there is no evidence of disease progression. There are no data directly comparing continuation using maintenance chemotherapy versus a switch to crizotinib after completion of this initial chemotherapy. The authors’ preference is to switch to crizotinib, rather than to use maintenance chemotherapy, because there are some patients who will deteriorate due to disease progression and thus miss the opportunity to be treated with an ALK inhibitor.

For patients who continue treatment with chemotherapy, crizotinib is indicated when there is evidence of disease progression. Factors that should be discussed with the patient in defining a treatment plan include the quality of the initial response to chemotherapy and the potential side effects of maintenance therapy.

ALK INHIBITORS: EFFICACY — Two tyrosine kinase (TK) inhibitors, crizotinib and ceritinib, have established roles in the treatment of anaplastic lymphoma kinase (ALK) fusion oncogene positive NSCLC, and additional agents are under development.

Crizotinib — Crizotinib is a multitargeted small molecule tyrosine kinase inhibitor, which was originally developed as an inhibitor of mesenchymal epithelial transition growth factor (c-MET); it is also a potent inhibitor of ALK phosphorylation and signal transduction [25]. This inhibition is associated with G1-S phase cell cycle arrest and induction of apoptosis in ALK-positive cells in vitro and in vivo [25]. Crizotinib also inhibits the related ROS1 receptor tyrosine kinase. (See "Personalized, genotype-directed therapy for advanced non-small cell lung cancer", section on 'ROS1 translocation'.)

Crizotinib induces rapid tumor regression and objective responses in the majority of patients whose tumors contain the ALK gene rearrangement [26].

The efficacy of crizotinib has been demonstrated in two randomized trials limited to patients whose tumors had the ALK rearrangement:

Previously treated patients − A phase III trial randomly assigned 347 patients who had previously been treated with one prior platinum-based chemotherapy regimen to either crizotinib or single agent pemetrexed or docetaxel [26]. Patients who were assigned to chemotherapy were allowed to be treated with crizotinib when they developed progressive disease.

At a median follow-up of 12 months, progression-free survival, the primary endpoint of the trial was significantly increased with crizotinib compared with chemotherapy (median 7.7 versus 3 months, hazard ratio [HR] for progression 0.49, 95% CI 0.37-0.64).

The objective response rate based upon independent radiologic review was also significantly increased (65 versus 20 percent). Responses were achieved more rapidly than with chemotherapy (median time to response 6.3 versus 12.6 weeks) and were of longer duration (32 versus 24 weeks).

There was no significant difference in overall survival (median 20.3 versus 22.8 months, HR for death 1.02). The absence of an overall survival benefit presumably reflects subsequent treatment since 64 percent of chemotherapy-treated patients had crossed over to crizotinib after progressing on chemotherapy.

Chemotherapy naïve patients − In a second trial, 343 chemotherapy naïve patients were randomly assigned to crizotinib or chemotherapy with pemetrexed plus either cisplatin or carboplatin [23]. In a preliminary report presented at the 2014 American Society of Clinical Oncology (ASCO) meeting, progression-free survival, the primary endpoint of the trial, was significantly prolonged with crizotinib compared with chemotherapy (median 11 versus 7 months, HR 0.45, 95% CI 0.35-0.60). The objective response rate was also significantly increased (74 versus 45 percent). The difference in overall survival was not significantly different (HR 0.82, 95% CI 0.54-1.26). However, the majority of patients assigned to initial chemotherapy subsequently were treated with crizotinib.

Treatment with crizotinib is generally continued until there is evidence of disease progression. The standard approach for patients with progressive disease is the use of the second generation ALK inhibitor ceritinib. In carefully selected patients (eg, an isolated site of recurrence that can be treated with local therapy, those with extremely mild and asymptomatic progression), crizotinib may be continued after initial evidence of progressive disease [27]. (See 'Ceritinib' below.)

Surgery and/or radiation therapy are the primary treatment modalities for patients with brain metastases from NSCLC, including those with the EML4-ALK fusion oncogene [28,29]. There are only limited data on the activity of crizotinib on brain metastases in this setting. (See "Overview of the clinical manifestations, diagnosis, and management of patients with brain metastases", section on 'Overview of management' and "Systemic therapy for brain metastases", section on 'Targeted agents'.)

Isolated brain metastases (a central nervous system [CNS] relapse without evidence of extracranial progression) may be a particular problem for patients treated with crizotinib. In this setting, continuation of treatment with crizotinib after treatment of the CNS relapse with surgery and/or radiation therapy may be associated with a significant period of control of extracranial disease [30].

Resistance to crizotinib — While crizotinib is highly active in patients with ALK-positive NSCLC, almost all patients develop resistance to the drug, typically within the first few years of treatment. Several distinct mechanisms of resistance have been reported in the literature.

In approximately one-third of resistant cases, tumors have acquired a secondary mutation within the ALK tyrosine kinase domain. The most common resistance mutation is the gatekeeper L1196M mutation, followed closely by the G1269A mutation. Other mutations occur at residues 1151, 1152, 1156, 1174, 1202, 1203, and 1206. The G1202R mutation is notable, as it confers high level resistance to crizotinib as well as to next generation ALK inhibitors (see below).

A second mechanism of crizotinib resistance is amplification of the ALK fusion gene. This can occur alone or in combination with a secondary resistance mutation.

Finally, a number of alternative or bypass signaling pathways have been shown to mediate crizotinib resistance. These include abnormalities in the epidermal growth factor receptor (EGFR), KIT, and insulin-like growth factor-1 receptor (IGF1R) pathways, and suggest the potential need for combination therapies to overcome resistance.

Ceritinib — Ceritinib is a second generation TK inhibitor of ALK that is approximately 20 times more potent than crizotinib. Ceritinib is indicated for patients who are resistant to or unable to tolerate crizotinib. Preclinical studies suggested that ceritinib had significant activity against cells that were either sensitive or resistant to crizotinib, including resistant tumors with the most common L1196M and G1269A resistance mutations.

After the maximum tolerated dose was established in the phase I study [31], ceritinib was studied in a dose expansion cohort of NSCLC patients with the ALK rearrangement [31,32]. Results from that expansion cohort were updated at the 2014 ASCO meeting [32]:

A total of 246 patients with ALK positive NSCLC were treated with ceritinib. Of these patients, 163 had previously been treated with an ALK inhibitor and 83 were ALK inhibitor naïve.

The objective response rate was 58 percent overall, 55 percent in those with prior crizotinib treatment, and 66 percent in ALK inhibitor naïve patients. The median duration of response was 10 months in the entire cohort, and 7.4 months in those with prior crizotinib treatment. The median progression-free survival for the entire cohort was 8.2 months, including 6.9 months for those previously treated with an ALK inhibitor and not estimable (lower bound of 95% CI 8.3 months) for those who had not previously received an ALK inhibitor.

Ceritinib was approved by the US Food and Drug Administration for patients who have progressed on or are intolerant of crizotinib [33].

Two phase III trials are currently recruiting patients with ALK-positive NSCLC, one in which ceritinib is being compared with single-agent chemotherapy after progression on a platinum-based doublet and on crizotinib (NCT01828112), and the other as first line treatment compared with a platinum-based doublet (NCT01828099).

Other second generation ALK inhibitors — Alectinib is another second generation ALK inhibitor that is under development.

In a multicenter, phase I/II study, 46 patients with ALK-positive NSCLC were treated with alectinib (CH5424802) at the phase II dose level (300 mg twice daily); none had received prior treatment with an ALK inhibitor [34]. An objective response was observed in 43 cases (93 percent), including two complete and 41 partial responses; 40 of the 43 responses were ongoing at data cutoff. Treatment was well tolerated.

In a second study, 47 patients were treated in a phase I/II study. All patients had progressed on or were intolerant of crizotinib [35]. Objective responses (including both confirmed and unconfirmed responses) were observed in 24 of 44 evaluable patients (55 percent) and 16 of 44 (36 percent) had stable disease. Eleven of 21 patients with brain metastases had an objective response (52 percent).

ALK INHIBITORS: TOXICITY — Treatment with the anaplastic lymphoma kinase (ALK) inhibitors crizotinib and ceritinib is generally well tolerated. However, there are a number of significant toxicities that may require dose modification or treatment discontinuation.

Gastrointestinal side effects — Nausea, vomiting, and diarrhea are common with both crizotinib and ceritinib, but are more severe with ceritinib. With crizotinib, less than 1 percent of these side effects were severe. However, more than one-half of patients treated with ceritinib required dose modification, and 9 percent required treatment discontinuation. (See "Enterotoxicity of chemotherapeutic agents", section on 'ALK inhibitors'.)

Hepatotoxicity — Liver function test abnormalities are occasionally seen with crizotinib and are commonly seen with ceritinib. Hepatoxicity can progress and may require dose modification or discontinuation. (See "Chemotherapy hepatotoxicity and dose modification in patients with liver disease", section on 'Crizotinib and ceritinib'.)

Pneumonitis — Severe, life-threatening, or fatal treatment-related pneumonitis has been reported in 1 to 4 percent of patients treated with either crizotinib or ceritinib. The development of pneumonitis should result in discontinuation of treatment with these agents. (See "Pulmonary toxicity associated with antineoplastic therapy: Molecularly targeted agents", section on 'Crizotinib and ceritinib'.)

Other toxicities that have been observed with crizotinib include the following:

Cardiac toxicity — Cardiac toxicity is relatively frequent with both crizotinib and ceritinib:

Sinus bradycardia is relatively frequent in patients treated with crizotinib and may be severe in some cases [36,37]. However, patients with sinus bradycardia were asymptomatic, and the bradycardia was not explained by other comorbidity or medications. Caution should be used in the concomitant administration of beta blockers in patients treated with crizotinib. (See "Cardiotoxicity of nonanthracycline cancer chemotherapy agents", section on 'Crizotinib and ceritinib'.)

QTc interval prolongation has been observed with crizotinib, and crizotinib should be avoided in patients with congenital long QT syndrome. Treatment should be temporarily discontinued if severe QTc prolongation develops and permanently discontinued if it recurs or is accompanied by an arrhythmia, heart failure, hypotension, shock, syncope, or torsade de pointes.

Our approach is to perform an EKG at baseline in all patients treated with either crizotinib or ceritinib. Subsequently, we check an EKG if the patient develops bradycardia (whether symptomatic or not) or if the patient is started on a drug that is known to cause QTc prolongation. (See "Cardiotoxicity of nonanthracycline cancer chemotherapy agents", section on 'Crizotinib and ceritinib'.)

Cytochrome p450 interactions — Both crizotinib and ceritinib are metabolized by cytochrome P450 CYP3A4. Thus, caution should be used when it is given concomitantly with CYP3A4 inhibitors, and care is required when these agents are coadministered with other agents that are predominantly metabolized by this system (table 1).

Visual disturbances — Visual disturbances were seen in 60 to 65 percent of patients treated with crizotinib in the phase II studies [20]. These were primarily associated with the transition from dark to light. Uncommon visual manifestations included photophobia, decreased visual acuity, and blurred vision. Similar symptoms have been reported with ceritinib, but their overall incidence is less that 10 percent.

Detailed ophthalmological assessment in over 200 patients from phase II experience with crizotinib did not demonstrate any objective abnormalities associated with visual symptoms [38]. However, optic neuropathy and blindness has been reported in one case, although that may have been related to prior whole brain radiation therapy [39].

Endocrine — Endocrine complications have been reported with both crizotinib and ceritinib.

With crizotinib, rapid depression of serum testosterone levels has been observed [40,41]. In a series of 32 patients treated with crizotinib, the mean serum testosterone level was below the lower limit of normal in 27 of 32 men (84 percent) compared with 6 of 19 (32 percent) among those not receiving crizotinib [41]. Levels of follicle stimulating hormone (FSH) and luteinizing hormone (LH) were also low, suggesting a centrally mediated mechanism. A large component of the lowered total testosterone may be due to significant depression of sex hormone binding globulin. Male patients who report symptoms of hypogonadism can be referred to endocrinology to discuss potential testosterone replacement. These findings require validation in larger cohorts. (See "Clinical features and diagnosis of male hypogonadism".)

Renal cysts — Renal cysts have been reported in 4 percent of patients treated with crizotinib [20]. These cysts may be complex, and the natural history of crizotinib-associated renal cysts is not known. The cysts may be positive on PET and can create confusion with renal metastases [42]. (See "Simple and complex renal cysts in adults".)

OTHER APPROACHES

Chemotherapy — Cytotoxic chemotherapy appears to have a similar level of activity in anaplastic lymphoma kinase (ALK)-positive patients with NSCLC compared with those with ALK-negative disease. The choice of a specific chemotherapy agent or regimen is based upon the same criteria applied in other cases of advanced NSCLC. When patients with ALK-positive advanced NSCLC require chemotherapy, pemetrexed or a pemetrexed-based regimen is generally preferred, since almost all of these patients have adenocarcinoma histology. (See "Advanced non-small cell lung cancer: Subsequent therapies for previously treated patients", section on 'Single agent chemotherapy' and "Systemic therapy for the initial management of advanced non-small cell lung cancer without a driver mutation", section on 'Effect of histology'.)

EGFR tyrosine kinase inhibitors — Patients with the ALK fusion oncogene do not appear to respond to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs). In a retrospective cohort of 19 patients with the ALK fusion oncogene, there were no clinical responses to EGFR TKIs, and the median time to progression was only five months [12].

SUMMARY AND RECOMMENDATIONS

The presence of an anaplastic lymphoma kinase (ALK) fusion oncogene defines a molecular subset of non-small cell lung cancer (NSCLC) with distinct clinical and pathologic features. The patients most likely to harbor ALK rearrangement are relatively young, never or light smokers with adenocarcinoma. (See 'Molecular pathogenesis' above and 'Clinicopathologic features' above.)

Whenever possible, therapy of patients with advanced NSCLC should be individualized based upon the molecular and histologic features of the tumor. If feasible prior to treatment, patients should have tumor tissue assessed for the presence of the ALK fusion oncogene, which is associated with sensitivity to ALK tyrosine kinase inhibitors, as well as other driver mutations such as those seen in the epidermal growth factor receptor (EGFR). (See "Personalized, genotype-directed therapy for advanced non-small cell lung cancer" and 'Chemotherapy versus targeted therapy' above.)

For patients with advanced or metastatic NSCLC whose tumors contain a characteristic ALK fusion oncogene, we recommend initial treatment with the ALK inhibitor crizotinib rather than chemotherapy (Grade 1B). There currently are insufficient data supporting the use of ceritinib as the initial ALK inhibitor. (See 'Crizotinib' above.)

Therapy with crizotinib should be continued until there is evidence of progressive disease. In carefully selected patients with an isolated site of recurrence that can be treated with local therapy or those with extremely mild and asymptomatic progression, crizotinib may be continued after initial evidence of progressive disease. (See 'Crizotinib' above.)

Crizotinib should not be used in patients without ALK rearrangement. In the United States, ALK-positivity must be demonstrated by fluorescence in situ hybridization (FISH) using the US Food and Drug Administration (FDA)-approved test (Vysis Probes) in accordance with the FDA label. In Europe, immunohistochemistry is widely used to detect ALK rearrangement. (See 'Crizotinib' above.)

Crizotinib is indicated as second-line therapy when progressive disease occurs for patients whose tumor contains the ALK fusion oncogene and initially were treated with chemotherapy. (See 'Crizotinib' above.)

For ALK-positive patients who develop resistance to crizotinib or who are unable to tolerate crizotinib, we recommend treatment with the second generation ALK inhibitor ceritinib (Grade 1B). (See 'Ceritinib' above.)

Chemotherapy is an appropriate option for patients who no longer respond to ALK inhibition. (See "Systemic therapy for the initial management of advanced non-small cell lung cancer without a driver mutation" and "Advanced non-small cell lung cancer: Subsequent therapies for previously treated patients".)

In some cases, chemotherapy is required before the results of molecular testing are available. If the tumor is found to contain the ALK fusion oncogene and patients have an ongoing objective response or stable disease after completing their initial doublet chemotherapy, the authors prefer to switch to crizotinib, although both crizotinib and single-agent maintenance chemotherapy are options. Factors that should be discussed with the patient in defining a treatment plan include the quality of the initial response to chemotherapy and the potential side effects of maintenance therapy. (See "Systemic therapy for the initial management of advanced non-small cell lung cancer without a driver mutation", section on 'Molecular characterization of tumor'.)

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