|Year : 2013 | Volume
| Issue : 2 | Page : 261-266
Efficacy of tyrosine kinase inhibitors in routine clinical practice: Epidermal growth factor mutations and their implications
Tanja Ovcaricek1, Tanja Cufer2, Izidor Kern2, Eva Sodja2, Aleksander Sadikov3
1 Department of Pulmonary medicine, University Clinic Maribor, Maribor, Slovenia
2 Department of Medical Oncology, Department of Pathology and Department of Molecular Diagnostics, University Clinic Golnik, Golnik, Slovenia
3 Department of Computer and Information Science, University of Ljubljana, Ljubljana, Slovenia
|Date of Web Publication||13-Jun-2013|
Oncology Institute Ljubljana, Zaloška cesta 2, 1000 Ljubljana
Source of Support: None, Conflict of Interest: None
Background: Activating mutations in the epidermal growth factor (EGFR) gene confer sensitivity to the tyrosine kinase inhibitors (TKIs) in patients with advanced non-small cell lung cancer (NSCLC). TKI treatment efficacy and EGFR mutation implications were evaluated in clinically selected advanced NSCLC patients treated with TKIs in routine clinical practice.
Materials and Methods: A retrospective chart review for clinicopathological characteristics and mutation status (EGFR, KRAS) analysis of 40 consecutive patients treated with TKIs between 2005 and 2010 was performed.
Statistical Analysis Used: PFS and OS were estimated by the Kaplan-Meier method, the log-rank test was used to test for differences. The strength of the associations between the EGFR mutation status and clinicopathological characteristics were tested with the Mann-Whitney U-test or the Kruskal-Wallis H-test.
Results: The prevalence of EGFR mutations was 45% with a predominance of deletion mutations in exon 19 (55.5%). Significant correlations between gender, histology, and EGFR mutations were observed. Median progression-free survival (mPFS) for the entire group of patients was 8.7 months and median overall survival (mOS) was not yet reached. Patients with EGFR mutant tumors derived significantly higher benefit from TKI therapy compared to patients with mutation-negative disease; with mPFS of 22.0 vs. 3.2 months (HR: 3.9, 95% CI 1.56-9.89) and with a trend towards better OS (probability of survival at 12 months 82.0 vs. 63.0%, P = 0.080).
Conclusion: We demonstrated that screening for EGFR mutations is reliable in a routine clinical setting and might allow for a better selection of NSCLC patients for anti-EGFR TKI therapy.
Keywords: Epidermal growth factor mutations, Non-small cell lung cancer, Routine clinical practice, Tyrosine kinase inhibitors
|How to cite this article:|
Ovcaricek T, Cufer T, Kern I, Sodja E, Sadikov A. Efficacy of tyrosine kinase inhibitors in routine clinical practice: Epidermal growth factor mutations and their implications. J Can Res Ther 2013;9:261-6
|How to cite this URL:|
Ovcaricek T, Cufer T, Kern I, Sodja E, Sadikov A. Efficacy of tyrosine kinase inhibitors in routine clinical practice: Epidermal growth factor mutations and their implications. J Can Res Ther [serial online] 2013 [cited 2019 Nov 22];9:261-6. Available from: http://www.cancerjournal.net/text.asp?2013/9/2/261/113379
| > Introduction|| |
Lung cancer is the leading cause of cancer death in the world. Non-small cell lung cancer (NSCLC) is the most common histological type and accounts for more than 80% of lung cancers. Third-generation platinum-based doublet chemotherapy has been a gold standard in the treatment of advanced NSCLC for a long time. Although a substantial proportion of patients experience improvement with platinum-based doublets, most remissions are usually short-lived with a median time to progression (mTTP) of around 8 months, and median overall survival (mOS) of around 12 months. , Notably, major progress in the understanding of the molecular biology of NSCLC led to the introduction of novel targeted therapies during the last decade.
The first evidence of targeted therapy efficacy in NSCLC came in the early 2000s with the invention of small-molecule inhibitors targeted to the tyrosine kinase (TK) domain of EGFR, such as gefitinib and erlotinib.  The results of initial studies demonstrated a marginal benefit in the overall NSCLC patient population; only a minority (approximately 10%) of unselected Caucasian NSCLC patients treated in second- or third-line therapy responded to tyrosine kinase inhibitors (TKIs); however, the responders experienced long-lasting remissions of many months or even years. , It became evident that there is a subset of NSCLC patients that might gain substantial benefit from TKI therapy. Female gender, non-smoker status, and adenocarcinoma histology have been initially recognized as the clinicopathological factors associated with better outcomes with TKIs ,,, and work on the molecular biology of NSCLC continued.
In 2004 two independent research groups simultaneously reported on activating EGFR mutations and confirmed their presence in dramatic responders to TKIs. , Since these discoveries, a number of retrospective molecular analyses performed within the framework of the pivotal prospective randomized studies comparing erlotinib/gefitinib vs. chemotherapy/placebo in second- or third-line settings for advanced disease have uniformly confirmed a predictive value of activating EGFR mutations for better response and improved progression-free survival (PFS) with both TKIs. ,, Subsequently, the predictive value of EGFR mutations for response to TKIs has also been confirmed in prospective randomized clinical trials. In the IPASS trial, the striking biologic effect of gefitinib in mutant tumors was evident based on remarkable differences in PFS observed among Asian patients with advanced NSCLC with and without EGFR mutations when treated with gefitinib (9.5 vs. 1.5 months, HR: 0.48, P < 0.001).  In the IPASS trial, the effect of TKI in EGFR wild-type patients was even detrimental compared to chemotherapy. Consequently, three prospective randomized studies confirmed significantly higher response rates to first-line gefitinib and more than a 50% improvement in PFS over cytotoxic therapy in selected EGFR mutation-positive Asian patients. ,, Similarly, significantly better response to another TKI, erlotinib, compared to chemotherapy was observed in the OPTIMAL trial conducted in selected EGFR-mutated Asian patients  and in the EURTAC study conducted in a European population.  In addition, as part of a large prospective Spanish observational study, a strikingly high objective response rate (ORR) (71%), median PFS (14 months) and median OS (27 months), was demonstrated in 350 Caucasian EGFR mutation-positive patients treated with TKIs in routine clinical practice. 
Even though the data from a large prospective randomized SATURN trial pointed to a positive effect of TKIs-namely, erlotinib in all NSCLC patients regardless of EGFR mutation status  -the results of subsequent subgroup analyses performed showed a much higher benefit of maintenance erlotinib in the EGFR mutant subgroup of patients.
The aim of our analysis was to evaluate treatment outcomes in clinically selected patients with advanced NSCLC treated with TKIs as first-line, maintenance, second- or third-line palliative therapy in our routine clinical practice before the era of routine EGFR mutation status determination. For all the patients included, retrospective determination of the EGFR mutation status of the primary tumor was performed and correlated with the treatment outcome.
| > Materials and Methods|| |
Between September 2005 and July 2010, a total of 40 patients with cytologically and/or histologically confirmed advanced NSCLC, treated with standard systemic therapy were included in our retrospective analysis. Adequate tumor material for determining the biomarkers (EGFR and KRAS mutations) and treatment with an anti-EGFR TKI in at least one line of systemic therapy for the metastatic disease were the sole inclusion criteria in this study. Biomarkers were determined retrospectively. Clinicopathological data, lifestyle characteristics (age, gender, smoking history), and data on systemic treatment were collected from the existing files.
Systemic treatment decisions were primarily based on consensus recommendations applied at our institute at the time. Most of the patients about 29 of them (72.5%) were treated with multiple lines of systemic therapy. All patients received the platinum-based doublets and at least one line of EGFR-directed therapy, either erlotinib or gefitinib. Three patients received two lines of TKI therapy. TKIs have been given as maintenance therapy after successful chemotherapy or as a separate line of systemic therapy. Although no special determination for specific population characteristics was mandatory, the patient population was enriched with regard to certain clinicopathological characteristics because the physicians were aware of a greater likelihood of benefit from TKI treatment in this patient population. Approximately one-third of the patients received TKI as first-line systemic therapy, prior to any chemotherapy; for the rest of them, TKI therapy represented second- or third-line systemic treatment; for almost half of them, it was given as maintenance therapy after platinum-based chemotherapy. [Table 1] shows the patient, tumor, and treatment characteristics of the entire cohort.
|Table 1: Patient, tumor, and treatment characteristics of the entire group of patients (n = 40)|
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EGFR and KRAS mutation status was assessed for all the patients in our study cohort. Forty lung-cancer patient samples from formalin-fixed paraffin-embedded tissue or cytological slide preparations, obtained by fine needle biopsies either of primary tumor or metastases or surgical resection of primary tumor, were retrospectively analyzed for predetermined biomarkers (EGFR, KRAS). Thirty-one (77.5%) of these were primary lung-tumor samples, six (15.0%) were lymph-node samples, and two (5.0%) were samples from other biopsy sites (distant metastases).
Genomic DNA was extracted from formalin-fixed, paraffin-embedded tissue sections and cytological slide preparations using the QiaAmp DNA FFPE tissue kit and the QiaAmp DNA Mini kit (Qiagen, Hilden, Germany) respectively, in line with the manufacturer's instructions. Quantification of extracted DNA was performed using a Qubit fluorometer (Invitrogen, Carlsbad, CA). For EGFR mutation analysis we used a commercially available kit, the TheraScreen EGFR29 Mutation Kit (DxS Diagnostics, Qiagen, Manchester, UK), which allowed for the detection of the following mutations: deletions in exon 19, insertions in exon 20, and substitutions L858R, L861Q, G719X, and S768I in the EGFR gene. All real-time PCR reactions were performed in a 25 μl final volume on the ABI 7500 instrument (Applied Biosystems).
For KRAS mutational analysis we used a commercially available kit, the TheraScreen KRAS Mutation Kit (DxS Diagnostics, Qiagen, Manchester, UK) which enabled the detection of mutations in codons 12 and 13 of the KRAS gene. All real-time PCR reactions were performed in a 25 μl final volume on the ABI 7500 instrument (Applied Biosystems).
The endpoints in this study were PFS and OS. PFS was calculated from the date of the start of TKI treatment, irrespective of the systemic treatment line and type of TKI therapy, to the date of lung cancer progression, the date of death from any cause, or the date of the last follow-up; censored observations correspond to patients alive and without evidence of disease progression at the time of the last follow-up. OS was calculated from the date of the start of the TKI treatment, again irrespective of the systemic treatment line and type of TKI therapy, to the date of death from any cause, or the date of the last follow-up; censored observations correspond to patients alive at the time of the last follow-up. PFS and OS as a function of the EGFR mutation status were estimated by the Kaplan-Meier method and the log-rank test was used to test for differences. The strength of the associations between the EGFR mutation status and patient and tumor characteristics were tested with the Mann-Whitney U-test or the Kruskal-Wallis H-test. Computations were performed with the use of the SPSS 16 statistical package. All reported P values are two-tailed.
| > Results|| |
Mutations in the EGFR gene were detected in a relatively high percentage of our patients (45%). The most prevalent mutation type was deletions in exon 19, followed by point mutations in exon 21. Mutation status and mutation types are depicted in [Table 2].
In the mutated subgroup of patients, a larger percentage of females and never-smokers were noted, when compared to the entire group; adenocarcinoma was revealed histologically in all the mutated cases. Patient, tumor, and treatment characteristics in EGFR-mutant patients are depicted in [Table 3].
|Table 3: Patient, tumor, and treatment characteristics in EGFR mutation-positive patients (n = 18)|
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An analysis of correlation between EGFR mutation status and clinicopathological features (gender, smoking status, and histology) revealed a significant correlation between EGFR mutations, female gender, and adenocarcinoma histology. Although not significant, there was an apparent trend showing a higher rate of EGFR mutations in never-smokers [Table 4].
|Table 4: Relationship between EGFR mutations and clinicopathological characteristics|
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We also determined the KRAS status and found KRAS mutations in only four out of 40 (10%) of the tumor samples. None of the tumors positive for KRAS mutations were positive for EGFR mutation.
The median follow-up from the initiation of TKI therapy was 14.5 months. Median PFS for the entire group was 8.7 months and median OS has not yet been reached. However, at median follow-up time of 14.5 months, the probability of overall survival was as high as 60% in our patient sample. The survival curves are depicted in [Figure 1] and [Figure 2].
|Figure 1: Progression-free survival of the entire population of patients|
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There was significant interaction between EGFR mutation status and TKI treatment with respect to PFS (P = 0.002). PFS was significantly longer among EGFR-mutant patients receiving TKI during any line of treatment compared to those without EGFR mutations (22.0 vs. 3.2 months, P = 0.002, HR: 0.26, 95% CI 0.10-0.66). [Figure 3] Probabilities of overall survival at 12 months were 82% for EGFR-mutated vs. 63% for the wild-type patients (P = 0.080, HR: 0.374, 95% CI 0.12-1.18). [Figure 4]
| > Discussion|| |
The results of our retrospective analysis, although performed on a limited number of advanced NSCLC patients, clearly showed that clinical selection of NSCLC patients for TKI therapy is not sufficient. Our patient population was enriched with regard to certain clinicopathological characteristics (females 45.0%, never-smokers 55.0%, adenocarcinoma patients 77.5%) due to the physicians awareness of a greater likelihood of sensitivity to TKI treatment in this patient population. Consequently, the frequency of EGFR mutations in this cohort of patients was high (45.0%). Yet, the median PFS after TKI therapy was modest in the whole group (8.7 months). However, the subset analysis according to EGFR mutation status revealed a significantly longer PFS after TKI in EGFR-mutated compared to EGFR non-mutated patients; 22.0 and 3.2 months, respectively. This renders the benefit of TKI therapy in EGFR mutation-negative patients characterized as such and treated in a routine clinical setting extremely modest and questionable.
Even though, it is well known that EGFR mutations appear more frequently with certain clinical characteristics ,,,, and significant correlations between female gender, adenocarcinoma histology, and EGFR mutation rate were seen in our study as well, we do not believe that these characteristics are sufficient enough for such mutations to occur; especially, if we consider that almost 17.0% of EGFR-positive patients in our study were males and 33.3% were current or former smokers. This is in line with the results presented by the Spanish group. Even though all the patients in the Spanish trial harbored EGFR mutations, a notable proportion of them were still males (30.0%) or former smokers (26.0%), or had a non-adenocarcinoma histology (9.0%). 
When stratified according to EGFR mutation status, a strikingly long median PFS of 22.0 months was obtained in mutated patients even though most of our patients received TKIs in second- or third-line systemic therapy (67%), after previous treatment with standard cytotoxic therapy. By reviewing the published literature one can find similar observations. The outcomes of EGFR-directed TKI therapy in EGFR mutation-positive patients are striking, with a more than 50% improvement in PFS over cytotoxic therapy in first-line therapy as well as in all subsequent lines of therapy. Compared with median PFS rates of 5 to 6 months achieved by standard chemotherapy, median PFS rates from 8 to 13 months obtained by EGFR-directed TKI therapy were reported in the EGFR mutated group of advanced NSCLC patients included in clinical trials. ,,,,,,
In our analysis a clinically meaningful difference in overall survival probability after TKI therapy between EGFR-mutated and EGFR wild-type patients has also been observed. Probabilities of survival at 12 months after TKI therapy were much higher for EGFR-mutated patients compared to wild-type patients (82.0% vs. 63.0%). These results support the observation that EGFR mutations not only predict a better response to TKIs, but carry a good prognosis as well. ,,, One must remember that in general patients with EGFR mutations respond better to chemotherapy compared to EGFR wild-type patients and that all our patients received at least one line of chemotherapy in addition to TKI therapy. It would be of great interest to analyze differences in outcome regarding the sequence of systemic therapy; that is whether EGFR mutation-positive patients would benefit from TKI therapy more if it were given upfront, before cytotoxic therapy or after it. As far as we know, as of yet there is no data available to answer this important question and unfortunately any meaningful analysis regarding this important issue was not able to be performed in our trial as well, due to the small sample size.
According to the available literature ,,, a higher sensitivity to TKI therapy has been observed in carriers of a specific EGFR mutation type; i.e. exon 19 deletion. Exon 19 deletion was the most prevalent mutation type in our group (55.5%) and seemed to be correlated with higher response rates (90% experienced a clinical response) compared to those patients with an insertion mutation in exon 21 (60% experienced a clinical response). However, the number of patients was far too small for any conclusion to be made. In any case, these results support further investigation in a larger sample of patients.
Only four patients in our study cohort were found to have KRAS mutations and none of them were positive for EGFR mutations, which is in line with the literature data showing that EGFR and KRAS mutations are exclusive. , Due to the small number of patients included in the analysis with only four (10.0%) of them expressing KRAS mutations, we could not perform any analysis of this subject.
In conclusion, our results show that a clinical selection of NSCLC patients based on clinicopathological characteristics does not allow for a proper selection of candidates for anti-EGFR TKI therapy. In addition, we demonstrated that screening for EGFR mutations is reliable in a routine clinical setting. While offering EGFR mutation-positive patients effective anti-EGFR TKI therapy, it can spare EGFR mutation-negative patients from ineffective and toxic therapy. Due to the small number of patients, we are unable to draw conclusions on outcomes with respect to additional markers of sensitivity and/or resistance to TKI therapy, such as specific EGFR mutations, KRAS mutation status, and other factors. To further fine-tune our treatment, additional research is needed to fully determine the predictive value of specific EGFR mutations and other molecular markers for resistance and/or sensitivity to particular EGFR-directed therapy.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4]