Hong Kong Respiratory Medicine

Drs Hoi-Yee Kwan1 and Tim Benepal2;
Department of Medicine, North District Hospital1; Department of Medical Oncology, St George’s Hospital and Medical School, London, UK2
Introduction
Lung cancer is the most common and is the leading cause of cancer-related mortality(1, 2). It is estimated that approximately 221,000 new cases (including both non-small cell and small cell lung cancers) will be diagnosed in the United States in 2011, and approximately 157,000 people will die of the disease(1). The International Agency for Research on Cancer of the World Health Organization (WHO) suggests that the disease accounts for more than 300,000 deaths in China every year(3). In Hong Kong, lung cancer is the commonest cancer in men and the third commonest in women. It is also the first leading cause of cancer deaths(4).

The overall 5-year relative survival rate for patients with lung cancer varies markedly depending on the stage at diagnosis, from 49% to 16% to 2% for patients with local, regional, and distant stage disease, respectively(5, 6). Non-small cell lung cancer (NSCLC), which comprises adenocarcinoma, squamous cell carcinoma, large cell carcinoma, and not otherwise specified (NOS) accounts for more than 80% of all cases of lung cancer(2, 5). At presentation, approximately one-third of all patients with NSCLC have locoregional disease that is too advanced for curative resection(2, 7). The optimal treatment for these patients depends on the full extent of disease, age, co-morbidities, and the patient’s performance status (PS). Currently, the combination of chemotherapy and radiotherapy (RT) is the standard treatment for patients with good PS, and where possible concomitant chemo-radiotherapy has been demonstrated to be the best therapeutic approach. Despite improvements in treatment, local tumor control remains suboptimal and distant metastases remain the major site of failure. More recently the discovery of novel therapeutic agents may have the potential to improve the current level of response and survival of locally advanced NSCLC patients(2, 5, 6).
With the advancement of new molecular techniques and better understanding of the biology of carcinogenesis, drug development has resulted in a number of agents with novel toxicity profiles that selectively target cancer cells, potentially affecting tumor growth and progression. Some of these agents have already been incorporated into the treatment of NSCLC, which will be reviewed in this article.

Epidermal growth factor receptor (EGFR) tyrosine kinase (TK) inhibitors
The EGFR belongs to a family of four closely related transmembrane protein receptors on epithelial cells (EGFR, HER-2, HER-3, HER-4). They exist as inactive monomers. Upon ligand-binding, they either heterodimerize or homidimerize, causing autophosphorylation of their TK domain, activating TK downstream signaling pathways, affecting cell proliferation and survival(8). EGFR is abundantly expressed in many solid tumors including NSCLC. Previously it was demonstrated that high levels of EGFR expression were associated with a poor prognosis in lung cancers(9). The identification of this family of receptors has driven a significant drug development program, resulting in a number of agents that are now in clinical practice.
i. Gefitinib
Gefitinib is an oral synthetic anilinoquinazoline which binds reversibly to the TK region of EGFR intracellular domain, thus blocking signal transduction pathways implicated in the proliferation and survival of tumor cells. Phase 1 studies demonstrated its activity in NSCLC(10). However subsequent phase 2 trials showed that significant response rates were only detected in a small percentage of recruited patients when it was given as a second or third line treatment for advanced NSCLC.
The first of these was the Iressa Dose Evaluation in Advanced Lung Cancer (IDEAL 1), a phase 2 trial in which most patients were recruited from non-US countries. The second was IDEAL 2, which was predominantly an American trial. In both studies, patients were randomly assigned to receive either 250mg or 500mg of gefitinib daily. Patients in IDEAL 1 showed an overall objective tumor response rates of 18.4% (95% CI 11.5% – 27.3%) among patients taking 250mg and 19% (95% CI 12.1% – 27.9%) among those taking 500mg. In IDEAL 2, the rate was 12% (95% CI 6% - 20%) among those who received 250mg gefitinib and 9% (95% CI 4% -16%) in those receiving 500mg. The difference in response rates between the two studies may have been due to the different percentage of EGFR mutations in the study populations. Toxicity profile was more favorable when gefitinib was taken at 250mg per day, with acne-like rash and diarrhea being the main adverse reactions(11, 12). Although the US food and Drug Authority (US FDA) granted a temporary but accelerated approval for gefitinib as a third-line treatment in May 2003, results from the Iressa Survival Evaluation in Lung Cancer phase III randomized placebo-controlled study (ISEL) revealed that gefitinib was not superior to placebo as a second-line or third-line therapy in unselected patients with stage IIIB and IV NSCLC(13). The addition of gefitinib to chemotherapy as the first-line treatment against advanced NSCLC showed no benefit in overall survival(14, 15). The registration of gefitinib was then withdrawn from the US FDA(16). Subsequent subgroup analysis of the ISEL study indicated that Asians, women and never smokers with adenocarcinoma histology seemed to respond better to gefitinib. However, tumor response was detected only in a minority of these selected subgroups, and correlation with the intensity of immunohistochemical staining of EGFR in the tumor cells proved unreliable(17).

In 2004, Lynch et al identified the presence of somatic mutations in the TK domain of the EGFR gene in eight out of nine patients with gefitinib-responsive lung cancer, compared with none of the seven patients who were resistant to gefitinib (p<0.001). The mutations were either a base-pair deletion in exon 19 (delE746-A750) or a point mutation in exon 21 (L858R)(18). In vitro, transfected mutant EGFR demonstrated both enhanced TK activity and increased sensitivity to gefitinib. It was hypothesized that the presence of a mutation stabilized the interaction between gefitinib and the kinase domain, thereby enhancing the inhibitory effect of the drug(18-20). The mutations do not appear to be induced by tobacco carcinogens, and are more common in patients with adenocarcinomas, and light (patients who smoke less than 100 cigarettes during their lifetimes) or never smokers(19-21). This discovery provides dramatic insight to the design of subsequent drug trials for targeted therapy, which will be discussed later in this article(22, 23).
The INTEREST trial was a randomised phase III trial to compare gefitinib with docetaxel in patients with locally advanced or metastatic non-small-cell lung cancer who had been pretreated with platinum-based chemotherapy. Only EGFR-gene-copy number was assessed among recruited subjects. Their EGFR mutation status was not assessed. The hazard ratio for overall survival for gefitinib was 1.02 (96% CI 0.905-1.150) which met the predefined non-inferiority criterion(24). Results were more impressive when similar studies were performed in phenotypically selected group of patients in a first line setting. The phase III Iressa Pan-Asia Study (IPASS) randomized 1217 patients with adenocarcinoma who were never or former light-smokers (those who quitted smoking for at least 15 years and had smoked ≤10 pack-years) to gefitinib or chemotherapy (carboplatin plus paclitaxel). The 12-month progression free survival (PFS) was superior in the gefitinib arm (24.9%) versus the chemotherapy arm (6.7%) (HR for progression or death 0.74, 95% CI 0.65-0.85; p<0.001). Among a subgroup of patients from both arms who harboured EGFR mutations (n=261), a even better PFS was achieved among those who received gefitinib (HR for progression or death 0.48; 95% CI 0.36 – 0.64; p<0.001); whereas in the subgroup of 176 patients who were EGFR wild-type, PFS was significantly longer among those who received chemotherapy (HR for progression or death with gefitinib 2.85; 95% CI 2.05 - 3.98; p<0.001). In the mutation positive subgroup, the objective response rate was 71.2% among those receiving gefitinib and 47.3% for those receiving chemotherapy (p<0.001), while that in the wild-type subgroup were 1.1% and 23.5% respectively (p=0.001). This study thus confirmed that the presence of certain EGFR mutations is a strong predictor of a better outcome with gefitinib upfront(25). This finding was validated by a phase III trial done by the North-East Japan Study Group (NEJ002), which randomized treatment-naïve patients with metastatic NSCLC and the presence of activating EGFR mutations prior to treatment to receive either gefitinib or chemotherapy (carboplatin/paclitaxel). The study was terminated early because planned interim analysis of data found a significantly longer PFS (primary end-point) in the gefitinib group than in the standard-chemotherapy group (10.4 months and 5.5 months respectively, p<0.001). A higher response rate (73.7% versus 30.7%, p<0.001) and median overall survival (30.5 months versus 23.6 months, p=0.31) were also found in the gefitinib group(26). Overall survival between treatment arms showed no statistical significant, which is possibly due to high cross-over use of gefitinib and chemotherapy in both groups(27). An identically designed study in Western Japan in first line patients with EGFR mutation compared gefitinib with chemotherapy (cisplatin/docetaxel). This further validated the results of NEJ002, showing very similar benefit in PFS and response rate(28).

ii. Erlotinib
Erlotinib is another reversible EGFR TK inhibitor similar to gefitinib. It was first approved by the US FDA in 11/2004 as a second- or third-line treatment for patients with locally advanced or metastatic NSCLC. On 16.4.2010, it further approved it as a maintenance treatment for patients with locally advanced or metastatic NSCLC whose disease did not progress after four cycles of platinum-based first-line chemotherapy(29).
In the BR.21 placebo-controlled randomized trial, 731 patients received either erlotinib or placebo as a second-line or third-line regimen. In the entire unselected population, the response rate was 8.9% in the erlotinib group and less than one percent in the placebo group (p<0.001). The median duration of response was 7.9 months and 3.7 months respectively. PFS and OS were significantly better in the erlotinib group (2.2 months and 6.7 months for erlotinib group, and 1.8 months and 4.7 months for placebo group respectively; HR 0.61; p<0.001)(30). Non-smokers with EGFR-expressing tumors and patients with bronchoalveolar carcinomas had better response rates. The presence and severity of rash appeared at that time to be surrogate marker for survival(30, 31). Out of the 731 recruited patients, EGFR expression was determined by immunohistochemistry in 325 patients; the number of EGFR genes as determined by fluorescence in situ hybridization (FISH) was analyzed in 221 patients; while EGFR mutational status was assessed in 197 patients. In multivariate analyses, adenocarcinoma (p=0.01), non-smokers (p<0.001), and EGFR expression as determined by immunohistochemistry (p=0.03) were associated with objective tumor response to erlotinib. Although the response rate among patients with mutant EGFR was more than twice of that among patients with wild-type EGFR (16% among patients with EGFR mutation vs 7% in patients with wild-type EGFR), the difference was insignificant (p=0.37). Among patients with higher number of EGFR genes, survival was significantly longer in patients received erlotinib than those received placebo (HR for death 0.44, 95% CI 0.23-0.82; p = 0.008). Likewise, survival benefit was observed among those with EGFR expression who received erlotinib compared with those received placebo (HR for death 0.68, 95% CI 0.63-1.36; P = 0.70). The risk of death did not differ significantly among patients with EGFR mutations in either treatment arm (HR for death 0.77, 95% CI 0.40-1.50; p=0.54), or among patients with wild-type EGFR who received either treatment (HR for death 0.73; 95% CI 0.49-1.10; p=0.13). However, multivariate analysis among all patients randomized into either treatment arm who had at least one EGFR test performed, the EGFR expression as determined by immunohistochemistry, the number of EGFR copies, and their EGFR mutation status were not significantly associated with survival. Thus erlotinib was shown to prolong survival in patients with advanced NSCLC after failure of first or second-line chemotherapy, and has become an approved treatment option in this setting. But it was not felt that mutational analysis at this time was necessary for patients who received EGFR inhibitors as second or third-line therapy(32).

The Sequential Tarceva in Unresectable NSCLC placebo-controlled phase III trial (SATURN) supported the use of erlotinib in NSCLC as a maintenance therapy. Patients who did not have progressive disease after given four cycles of platinum-based chemotherapy were randomly allocated to receive erlotinib or placebo. The co-primary end-points were firstly PFS in all analyzable patients (n=437 in the erlotinib group; n=447 in the placebo group) irrespective of their EGFR status, and secondly PFS of patients whose tumors, as determined by immunohistochemistry, had EGFR protein over-expression (n=307 in the erlotinib group; n=311 in the placebo group). The median PFS was significantly longer with erlotinib (12.3 weeks) than with placebo (11.1 weeks) for all patients (HR0.71 95% CI 0.62 – 0.82; p<0.001). Among patients with EGFR over-expression, PFS was also significantly longer in the erlotinib group (12.3 weeks) than the placebo group (11.1 weeks) (HR 0.69, 95% CI 0.58-0.82; p<0.0001). Pre-planned biomarker analyses for EGFR mutation status also showed that erlotinib was active both in patients with EGFR-mutants (HR 0.10, 95% CI 0.04-0.25; p<0.001) and in those with wild-type EGFR (HR 0.78, 95% CI 0.63-0.96; p=0.0185). Comparing these two subgroups of patients, greatest benefit in PFS from erlotinib was observed among those who were EGFR mutation-positive. Overall survival was significantly prolonged in the erlotinib group (12 months) compared with the placebo group (11 months) in the overall unselected population (HR 0.81, 95% CI 0.70-0.95, p=0.0088). Similar benefit was observed among the EGFR immunohistochemistry-positive population (HR 0.77, 95% CI 0.64-0.91; p=0.0063) and among patients with wild-type EGFR (HR 0.77; 95% CI 0.61-0.97; p=0.0243). The overall survival of EGFR mutation-positive patients was not significantly improved in the erlotinib group (HR 0.83, 95% CI 0.34-2.02; p=0.6810), which could be due to high degree of censoring and the extensive cross-over rate (67%) to second-line EGFR TKI therapy in the placebo group of this population.
In further subset analysis, the overall survival with maintenance erlotinib was statistically significant in patients who had stable disease after first-line chemotherapy (median OS 11.9 months in the erlotinib group; 9.6 months in the placebo group; HR 0.72, 95% CI 0.59-0.89; p=0.0019), compared with those having previous complete or partial response with first-line chemotherapy (median OS 12.5 months for the erlotinib group vs 12.0 months for the placebo groups; HR 0.94, 95% CI 0.7-1.20; p=0.618). The treatment was well tolerated. This is the first study to show that giving maintenance therapy with a targeted agent to patients with advanced NSCLC immediately after they have completed conventional first-line platinum-based chemotherapy can significantly prolong their PFS and OS. Thus it demonstrated that first-line maintenance therapy with erlotinib could be considered in patients who do not progress after four cycles of chemotherapy, particularly in the subset of patients with stable disease(33).
Concurrent use of erlotinib with platinum doublets in first-line setting in unselected NSCLC patients did not prolong survival(34, 35). But when administered as a first-line or second-line therapy to patients with known EGFR mutations and advanced NSCLC, erlotinib achieved a response rate of 70.6%, as revealed by a single-arm trial launched by the Spanish Lung Cancer Group. Time to progression (TTP) and OS were 14 and 27 months respectively(36). The OPTIMAL study conducted in China showed encouraging results with the use of erlotinib as a first-line treatment in advanced NSCLC, in patients positive for activating EGFR mutations. In this open-label, randomised, phase III trial conducted in 22 centres in China, patients with stage IIIB/IV NSCLC and a confirmed activating EGFR mutation were randomly assigned to receive erlotinib (n=82) or gemcitabine plus carboplatin (n=72). PFS was significantly superior in erlotinib arm (13.1 months in erlotinib arm compared with 4.6 months in chemotherapy arm; HR 0.16, 95% CI 0.10-0.26; p<0.0001). More patients from the chemotherapy group experienced grade 3 or 4 toxicity and treatment related serious adverse events(37) . These two studies clearly showed the feasibility and importance of EGFR mutation testing in a larger population and multi-centre setting, and supported patient selection according to the genotype rather than phenotype alone(38). Interim results from EURTAC (European Randomised Trial of Tarceva vs Chemotherapy) are also encouraging. It is the first phase III trial to compare erlotinib with platinum-based chemotherapy as first line treatment in advanced NSCLC patients with EGFR mutations (n= 174) conducted in a Western population. Progression free survival (primary end-point) was 5.2 months in chemotherapy arm (95% CI 4.4 – 5.8 months) and 9.4 months (95% CI 7.9 – 12.3) in the erlotinib arm respectively (HR 0.42; p<0.0001). Response rate among patients in erlotinib arm is more superior to those in chemotherapy arm (p<0.0001), as well as the median survival (HR 0.80; p = 0.42)(39). However, the response rate of 54.5% is not as high as that observed in Asian populations (83% from the OPTIMAL trial)(37, 39). Final results are pending(39).
A recent phase II trial failed to show any benefit of combining chemotherapy and erlotinib in patients with advanced NSCLC and the presence of high EGFR protein expression or gene copy number, further demonstrating the importance of determining the EGFR mutation status of patients with advanced NSCLC before initial therapy, which could be done within a clinically relevant time-frame (< 5 working days). The 6-month PFS of either treatment arms (erlotinib alone, or chemotherapy plus erlotinib) were less than the historical control, thus failed to meet the primary end-point. Patients with tumors harboring EGFR activating mutations fared better on erlotinib alone with a superior response rate, PFS and OS, compared with the dual treatment arm. In the wild-type EGFR patients, survival curves in the two treatment arms nearly overlapped. This study thus provides insight to the direction of developing personalized medicine by performing molecular analysis of tumor tissue obtained before therapy to select the best treatment(40).

iii. Cetuximab
Cetuximab is a chimeric human-mouse IgG1 monoclonal antibody that neutralizes the extracellular EGFR domain by attaching to specific proteins(5, 6). It has been approved by FDA in the treatment of squamous cell carcinoma of head and neck on 1st March 2006, and in combination with irinotecan for the treatment of EGFR-expressing metastatic colorectal carcinoma in patients refractory to irinotecan-based chemotherapy on 12th February 2004(41). Results from phase II and phase III trials at the first-line setting when combined with chemotherapy against advanced or metastatic NSCLC have been controversial. A meta-analysis evaluated four eligible RCTs that included more than 2000 patients suggested that the addition of cetuximab to first-line platinum-based chemotherapy in this setting produced significant clinical benefit with acceptable toxicity. It led to significant improvement in OS [HR 0.87 (CI = 0.78-0.96); p=0.005) and objective response rate [OR 1.48; 95% (CI = 1.22-1.80); p<0/001], although no significant improvement in PFS is observed [HR 0.91 (CI = 0.83 – 1.00); p=0.006]. More cetuximab-related toxicities were reported, in particular diarrhea, asthenia, skin toxicity, influsion-related reaction and hypokalaemia(42). Further research is needed to identify markers predictive of cetuximab benefit in NSCLC(42) .
 

2. Inhibitors of angiogenesis
Neoangiogenesis, i.e. the formation of new blood vessels through proliferation of vascular endothelial cells, plays an important role in the growth of malignant tumors, their ability to invade surrounding tissues and systemic dissemination. A family of vascular endothelial growth factors (VEGF), including VEGF-A, VEGF-B, VEGF-C, VEGF-D and placental growth factor, are the key circulating proteins that promote vascularization. Targeting the VEGF ligand-receptor system is a very promising treatment as they are chiefly localized on malignant endothelium. Through inhibiting the VEGF-VEGFR pathways, it reduce blood supply to tumor cells and suppress their growth(43, 44).

One example is bevacizumab, which is a combinant humanized monoclonal antibody that blocks VEGF binding to its receptor. It is the only approved anti-angiogenic therapy for treatment of advanced NSCLC at present(5). Approval of the use of bevacizumab as a first line agent for NSCLC was granted in 2006, with reference to results from a phase III US study (E4599), in which 878 chemonaive patients with stage IIIB or IV NSCLC were given chemotherapy with paclitaxel and carboplatin plus bevacizumab, or paclitazel and carboplatin alone(6, 45). Patients with squamous cell carcinoma, haemoptysis and brain metastases were excluded, based on the results from a previous phase II trial that these patients are more prone to bleeding risks which could be fatal(46). Significant survival benefit was observed in groups receiving bevacizumab in addition to chemotherapy (median survival 12.3 months in chemotherapy plus bevacizumab group vs 10.3 months in chemotherapy-alone group, p=0.003). A significant increase in progression-free survival (6.2 months vs 4.5 months in the two groups respectively, p<0.001), with corresponding response rates of 35% and 15% (p<0.00) respectively were found. There were fifteen treatment-related deaths in the chemotherapy plus bevacizumab group, including five from pulmonary hemorrhage, compared with only two cases in patients receiving chemotherapy only(45). Another randomized phase III trial (Avastin in Lung Cancer, AVAiL) aimed to compare two different doses of bevacizumab (7.5mg/kg and 15mg/kg) plus gemcitabine/cisplatin, with placebo plus gemcitabine/cisplatin. There was a small but significant improvement in PFS (6.7 vs 6.5 vs 6.1 months respectively) and response rate (34.1% vs 30.4% vs 20.1% respectively), but without a significant difference in OS (13.6 vs 13.4 vs 13.1 months respectively), probably due to high use of post-study second-line treatment, as reflected by the fact that the authors changed the primary endpoint from OS to PFS after study initiation. A higher rate of pulmonary hemorrhage of all grades was also observed(47). A systematic review and meta-analysis published in 2011 evaluated the strength of data on the efficacy of adding bevacizumab to chemotherapy in advanced NSCLC. Results from five RCTs with a total of 2252 patients using platinum-based chemotherapy regimens were analyzed. Compared to chemotherapy alone, the addition of bevacizumab to chemotherapy resulted in a significantly longer OS [HR 0.89 (95% CI 0.79-0.99); p=0.004], longer PFS [HR 0.73 (95% CI 0.66 – 0.82); p<0.00001] and higher response rates [OR 2.34 (95% CI 1.89 – 2.89); p < 0.00001], but there was at the same time increase in toxicities and treatment-related mortality in bevacizumab group [OR 1.82 (95% CI 1.04 – 3.18); p=0.04](48). Use of bevacizumab could be a treatment option but not mandatory for all patients with advanced stage NSCLC(5). At the moment, bevacizumab is considered to be a standard of care for chemonaive, advanced, nonsquamous NSCLC in the USA, but not in the UK(6, 49). Owing to the risk of cerebrovascular bleeding and haemoptysis, bevacizumab is contraindicated in patients with brain lesions (unless previously treated) or squamous tumors(5, 6). There are further ongoing studies to evaluate the safety and efficacy of combining bevacizumab with other chemotherapeutic agents in advanced NSCLC(6).

3. Anaplastic lymphoma kinase (ALK) inhibitors
ALK encodes a tyrosine kinase that is normally expressed in neuronal cells. EML4 (echinoderm microtubule-associated protein-like 4) - ALK is an oncogene comprising N-terminal portion of the EML4 gene and C-terminal portion of the ALK gene, as a result of small inversion within the short arm of chromosome 2(50). The fusion transcript was first identified in a subset of NSCLC patients, who are distinct from those having EGFR mutations(50, 51). It promotes cell growth and inhibits apoptosis. Transgenic mouse lines that express EML4-ALK specifically in lung epithelial cells developed hundreds of adenocarcinoma nodules in both lungs within few weeks after birth, while administration of ALK inhibitor cleared the tumor burden and improved their survival, thus confirming the role of EML4-ALK in the carcinogenesis of NSCLC(52). This and other fusion-type proteins are thought to be present in about 2-5% of patients with NSCLCs, who are relatively young, and are more likely to be never or light-smokers (<10 pack-years), and are predominantly adenocarcinomas(51).

Crizotinib is an oral ATP-competitive selective inhibitor of the ALK and mesenchymal-epithelial transition factor (MET) tyrosine kinases. It inhibits tyrosine phosphorylation of activated ALK in a concentration dependent manner(53). A multi-centre phase 1 trial of crizotinib was published in 2010. Eighty-two patients with ALK-rearranged advanced non-small-cell lung cancer received oral crizotinib 250mg twice daily for a mean treatment duration of 6.4 months. More than 90% of them had received treatment for lung cancer previously. The overall response rate was 57% according to Response Evaluation Criteria in Solid Tumors (RECIST). Twenty-seven patients (33%) had stable disease, 46 patients had a partial response, and one patient had complete response. All patients were tested negative for MET amplification, suggesting that the therapeutic effect of crizotinib was through inhibition of ALK alone. The estimated probability of progression-free survival at 6-months was 72%. Toxicity was mild and the drug was well tolerated in general. The most commonly reported side effects were grade 1 nausea and diarrhea (50%). Mild visual disturbances, typically reported as having trials of light following objects moving relative to the observer, occurred in 41% of patients. Grade 3 to 4 liver derangement was detected in nine patients (11%). Treatment was discontinued in one patient with grade 3 elevation in alanine aminotransferase (ALT) because of recurrent grade 3 liver derranagement despite dose reduction(51).

Yet, a certain number of ALK-positive patients are refractory to crizotinib from the start of treatment, or become resistant after an initial response(51, 53). This could be due to mutations developed before or during treatment(54). Choi et al described two de novo mutations, C1156Y and L1196M mutation, within the kinase domain of EML4-ALK in tumor cells isolated from a patient who developed rapid disease progression after five months of crizotinib, despite initial partial response. Drug sensitivity was markedly reduced in cells expressing either mutation, leading to crizotinib resistant, and probably to other ALK inhibitors also. Although it is likely that the mutations were secondary mutation, it could not be confirmed because sites of specimens obtained from the patient before treatment and after stopped crizotinib were different (sputum sample and pleural fluid respectively). The resistant clones may have been present before treatment. It still provides basis for the future development of next-generation ALK inhibitors possessing the ability to eradicate tumors that harbor EML4-ALK with acquired mutations(53).

Though an uncommon mutation, its presence in a highly prevalent disease like lung cancer still reflects a substantial number of potential candidates that would benefit from this targeted kinase inhibition(54, 55). In August 2011, the FDA granted accelerated approval to crizotinib for the treatment of locally advanced or metastatic ALK-positive NSCLC (56). A multi-centre Phase II trial is ongoing. In PROFILE 1005, crizotinib was given to patients with ALK-rearranged advanced NSCLC who developed disease progression despite previous chemotherapy. Initial results found that 83% patients had target lesion shrinkage after an median treatment duration of 9 weeks. Seven patients have disease progression by RECIST. Most frequently reported drug toxicities are grade 1-2 nausea (46%), vision disorder (45%), vomiting (39%), and diarrhea (29%). Fifteen percent patients reported grade 3-4 toxicities, including raised ALT, dyspnea and neutropenia. Two treatment-related deaths were found, one due to pneumonitis while another died due to unknown cause. Quality of life could be maintained in majority of patients. Most of them reported clinically significant improvement in symptoms after treatment. Final results are expected in 2012(57).


4. Combining targeted agents
Studies have been done to assess for additional benefit by combining different agents with multiple, functionally linked, inhibitory properties. Results so far have been disappointing. BeTa is a phase III trial that randomized enrolled patients, who failed first line treatment for advanced NSCLC, to receive erlotinib plus bevacizumab (bevacizumab group) or erlotinib plus placebo (control group). The overall survival (primary endpoint) did not differ significantly between the two groups (hazard ratio 0.97, 95% CI 0.8-1.18, p=0.7583), while more patients in the bavacizumab group had serious adverse event than control group (42% vs 36% respectively)(58).

Addition of tivantinib, a competitive small molecule MET inhibitor, to erlotinib did not show significant improvement in median PFS compared with erlotinib plus placebo in patients with previously treated but EGFR TKI naïve advanced NSCLC(59). Further studies of this combination are planned. as it may benefit patients with EGFR TKI resistance. High-level MET amplification, though rare, is an established mechanism of resistance to EGFR TKIs among patients with EGFR-mutant NSCLC and is associated with poor prognosis(43, 59). MET inhibition by a monovalent monoclonal antibody (MetMAb) has also been tested in NSCLC (60-64).


5. Targeted therapy & RT
Preclinical and clinical results indicate that EGFR can mediate radio-resistance in different solid human tumors since radiation appears to amplify the EGFR pathway. Combining RT and EGFR inhibitors may improve local tumor control compared to irradiation alone. The underlying mechanism is still unclear. Further research is required to establish the exact relationship between EGFR and radiosensitivity(2).
Several clinical trials combining EGFR inhibitors with radiation in locally advanced lung cancer has been published. The SCRATCH trials provided evidence to support the safety of combining cetuximab to RT in patients with stage III NSCLC(65). The Radiation Therapy Oncology Group conducted a phase II study of cetuximab, carboplatin, paclitaxel, and radiotherapy in unresectable stage III NSCLC (RTOG 0324). Ninety-three patients received cetuximab at conventional doses with six cycles of standard weekly paclitaxel and carboplatin, and concurrent radiation therapy. The treatment was reasonably well tolerated with a response rate of 62% (n=54) and with a 12-month overall survival of 68%(2, 66). However, the phase II study conducted by the Cancer and Leukemia Group B found that addition of cetuximab to pemetrexed, carboplatin, and thoracic radiation in patients with previously untreated stage III NSCLC did not confer additional benefit in patients’ 18 month survival rate(2, 67).
Although the CALGB 30106 trial demonstrated the feasibility of concurrent use of gefitinib and RT or chemoradiotherapy, the efficacy of such treatment regime needs further research(2, 68). The CRITICAL study is a phase I study to evaluate the combination of gefinitib with concurrent chemoradiotherapy. The treatment was well-tolerated, but loco-regional progression was the major cause of treatment failure in 16 out of 28 patients enrolled into the study(69). The JCOG0402 study conducted by the Japan Clinical Oncology Group evaluated the safety and efficacy of administering cisplatin plus vinorelbine followed by gefitinib and thoracic RT to patients with unresectable locally advanced NSCLC. They concluded that the treatment regimen effective among highly selected patients with acceptable toxicity. However it must be stressed that the results did not meet the study endpoint(70).

The addition of erlotinib to RT demonstrated activities without increasing toxicities(2, 71) . In a prospective randomized phase II study, erlotinib was administered in addition to thoracic RT in patients with unresectable stage I-IIIA NSCLC who are not suitable to receive chemotherapy. The response rate was 55% for those received RT alone, and 83% for those received concomitant erlotinib and RT(71). Further studies are required to confirm its efficacy. At the moment, the optimal integration of targeted therapy into current chemoradiation paradigms has yet to be determined(2).


6. Conclusion & future directions
The development of lung cancer treatment has now been focused on personalized therapy. Attempt should always be made to obtain adequate tumor tissue (i.e. biopsy) for determining the histological subtype, and genotyping for EGFR and other gene mutation status(51, 54, 72). It is foreseen that treatments will be guided by these molecular biomarkers in the future(72). This will impose changes to our diagnosis and management of lung cancer. The use of genotyping as standard clinical practice should be considered to guide the selection of appropriate targeted therapy(73, 74). Many different targeted therapies have been investigated in NSCLC. It is likely that through continuing drug development more novel molecular agents will be available in the years to come.


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