Background of the need for targeted therapy opt i ons and plat i num-based therapy responses i n EGFR and ALK-mutated lung adenocarc i noma

Aim: To present our experience in EGFR and EML-4/ALK-mutated lung adenocarcinoma patients. Material and Methods: 2580 patients were retrospectively evaluated. Only stage-4 lung adenocarcinoma patients who treated with at least 2-cycles of platinum-based regimens at frontline were included. Results: Among 105 eligible patients, EGFR and EML-4/ALK mutations was detected in 14 and 4 patients. 75 were wild-type for both mutations. The median age and age of diagnose was 61 and 58.5, respectively. 81% was male and 78% was smoker. EGFR and EML-4/ALK-mutant patients were predominantly female and non-smoker (EGFR; p=0.025 and 0.002, EML-4/ALK; p=0.003 and 0.012,respectively). EML-4/ALK-mutant patients were significantly younger than EML-4/ALK wild-type (p=0.02) (Table 1). EGFR exon-19, 20 and 21 mutations were associated with liver, bone and pleural metastases, respectively (p=0.046, 0.05 and 0.035,respectively). After firstline platinum-based chemotherapy, complete remission (CR) and partial remission (PR) rates were 4.7% and 24.6%,respectively. Concurrent radiotherapy and absence of bone metastases at diagnosis were significant factors influencing firstline platinum-based therapy responses (p=0.004 and p=0.046,respectively). EGFR or EML-4/ALK mutation status didn’t show significant difference in terms of platinum-based treatment response (p=0.933 and 0.184,respectively). Median progression-free survival (PFS) was 10 months. The observed effect of concurrent radiotherapy and the presence of bone metastases on treatment response didn’t reflected in the PFS results (p=0.079 and 0.285,respectively). Conclusion: The presence of EGFR and ALK mutations does not effect the treatment response of platinum-based regimens. The association of EGFR exon subsets with metastasis points is worth investigating.


Introduction
Primary lung cancer is the second most common malignancy after non-melanoma skin cancer and is the most common cause of malignancy related death.Non-small cell lung cancers constitute 80-90% of primary lung cancers and due to the decrease in tobacco use in recent years, the frequency of squamous cell type has decreased while the adenocarcinoma type has become dominant [1].Frontline platinum-based therapy response rates for lung adenocarcinoma have been reported to range from 30 to 40%.[2].To increase these low response rates, EGFR and ALK gene mutations have emerged as important focal points in the development of targeted therapies.
Increased tyrosine kinase activity resulting from mutations effecting the tyrosine kinase domain of EGFR and inversion of the short arm of the chromosome 2, which causes the fusion of the ALK gene with the EML-4 gene, play an important role in the etiopathogenesis of non-small cell lung cancer.Therefore, current guidelines recommend routine screening of these genes regardless of the clinical status [1,3].
In this study, based on the rarity of these mutations and studies with limited number of patients, we aimed to present our single center experience and make a contribution to the literature.

Results
Among 105 eligible patients, 14 patients harbored EGFR gene mutations while EML-4/ALK transfusion was detected in 4 patients.75 patients were wild-type for both mutations.
Median age of entire cohort was 61 while median age of diagnose was 58.5.81% was male and 78% was smoker.The most frequent metastasis sites were bone (38%), brain (35%) and contralateral lung (32%) (Table 1).Table 1.Demographic and clinical results (WT/WT: Wild-type for EGFR and EML4/ALK mutations).All p values belong to the comparisons of the cases carrying gene mutations with the WT/WT group.
After firstline platinum-based chemotherapy, complete remission (CR) and partial remission (PR) rates were 4.7% and 24.6%, respectively.Stable disease status was observed in 4.7% while 66% of patients showed progression.Concurrent

Discussion
Lung cancer is still among the most common cancers but with the decrease in tobacco use and the addition of targeted therapy agents to conventional chemotherapy regimens, a halving of incidence and mortality rates has been observed in the last two decades [12].As the details of the cancer Frequencies of EGFR and EML-4/ALK transfusion gene mutations in lung adenocarcinoma were reported as 10-20% and 2-5%, respectively [1].Patients harbouring these mutations are presenting a different clinical profile compared to wild types.Most studies showed that, EGFR and EML-4/ALK-mutated lung adenocarcinoma patients are mostly non-smoker females and also EML-4/ALK positive patients are significantly younger [4][5][6]7].Results of our cohort were consistent with these findings.
In our study, EGFR mutant patients were unable present significant difference regarding response to platinum-based chemotherapy, PFS or OS comparing EGFR wild-type patients.
The only significant factors improving platinum-based treatment results were concomittant RT and absence of bone metastasis at diagnose (p=0.004 and 0.046, respectively).Also some other studies evaluating platinum-based chemotherapy response from the perspective of EGFR gene mutation also declared ~30% treatment response, but no statistically significant difference was found in treatment response, PFS and OS between mutated and wild-type patients [13][14][15].
In another article evaluating 162 lung adenocarcinoma patients [8], of which 40 were EGFR-mutated, platinum-based frontline therapy responses were comparable between EGFR-mutated and wild-type groups (43.5% vs. 23.9%,p=0.072).PFS and OS durations of EGFR-mutated and wild-type patients were also did not able to show significant difference between groups (p=0.69 and p=0.069, respectively).In this study only 9 patients were carrying classical EGFR mutations (exon 18, 19 and 21 mutations) while remaining 31 patients were positive for other EGFR mutations.Subanalysis of classical EGFR-mutated patients showed similar PFS duration (p=0.81)but better platinumbased therapy response (p=0.021) and improved OS duration (p=0.028)comparing wild-type patients.Although the small number of patients, the presence of EGFR gene mutation was declared as an independent favorable prognostic factor for platinum-based treatment response and overall survival [8].
EGFR gene mutation was found to be associated with brain, bone and pleural metastases in the REASON study [5] from Germany, which consisted of 432 EGFR gene mutation-positive cases.We also found a possible correlation between Exon 19, 20 and 21 mutations with liver, bone and pleural metastases, respectively.However, it was impossible to make a definitive interpretation due to the insufficient number of patients.
The presence of EML-4/ALK transfusion stands out as a negative factor for patients.In the study of Mayo Clinic [6], 266 EML-4/ALK negative non-small cell lung cancer cases compared to 34 EML-4/ALK-mutated patients and EML-4/ALK positivity declared as a negative predictive factor for progression/relapse-free survival [6].Koh et al. [9]  First generation TKIs, gefitinib and erlotinib, were unable to show significant OS benefit with over platinum-based regimens but OR and PFS rates were significantly improved [1].In the light of these results, and with their safe use even in patients with low performance scores, TKIs have become the backbone of EGFR-mutated lung adenocarcinoma patients.Following these agents, afatinib and dacomitinib emerged to the market as second generation TKIs.Osimertinib, thirdgeneretion TKI, proved itself in the FLAURA study [11] with its PFS contribution against 1st generation TKIs and its superior response results in cases with CNS metastasis.Moreover, with the statistically significant contribution to OS (38.6 vs 31.8 months, p=0.046), the current guidelines are recommending asimertinib as preferred therapy in firstline treatment of patients with sensitizing EGFR mutations [1,3].Crizotinib was the first targeted therapy improving OR and PFS rates of EML-4/ ALK rearranged patients comparing platinum-based therapies.
Ensartinib and lorlatinib also stand out as ALK inhibitors whose phase 3 studies are ongoing and are expected to be included in daily clinical practice in the near future [1].
Although targeted therapies have considerably increased the OR and PFS results compared to platinum-based therapies, there is still a need for new agents to prolong the duration of OS.

Conclusion
The presence of EGFR and ALK mutations does not effect the treatment response of platinum-based regimens according to current literature and our study.Retrospective study design and low numbered subgroups in EGFR and EML-4/ALK mutated patients are the limitations of our study.Although these limitations, the association of EGFR exon subsets with metastasis points is worth investigating, as demonstrated in REASON study [5].

Disclosure
The study was not supported by any individual, institution or organization.It does not contain any conflict of interest.
radiotherapy (RT) and absence of bone metastases at diagnosiswere statistically significant factors influencing firstline platinum-based therapy responses.Concurrent radiotherapy with platinum based chemotherapy (n=35) showed significantly superior treatment response rates comparing patients who did not recieve radiotherapy (p=0.004).Relaps rates of patients with and without bone metastasis were %77.5 and.%58.5 after platinum based therapy, respectively (p=0.046).EGFR or EML-4/ALK gene mutation status did not able to show any significant difference in terms of platinum-based treatment response (p=0.933 and 0.184, respectively).The effect of EGFR exon mutations on treatment response or survival results did not performed due to low numbered subgroups.Median progression-free survival (PFS) duration of entire cohort was 10 months.Median PFS durations of EGFR, EML-4/ALK and WT/WT groups were also comparable which were 10.8, 12 and 10.2 months, respectively (p=0.506) (Figure1).The observed effect of concurrent radiotherapy and the presence of bone metastases on treatment response is not reflected in the PFS results (p=0.079 and 0.285, respectively).Brain metastasectomy was performed in 8 (21.6%) of 37 cases with brain metastases and no positive effect was detected in terms of PFS and treatment response rates (p=0.127and p=0.465).Estimated overall survival (OS) rate of entire cohort was 17% at first year.

Figure 1 .
Figure 1.Cumulative PFS of entire cohort (a) and mutation groups (b).
development process are clarified, new possibilities for treatments emerge.Point mutations in exon 18 and 21, Exon 19 deletion and Exon 20 insertion of the EGFR gene effect the receptor tyrosine kinase domain of the transmembrane cell receptor protein.Similarly, translocation of the ALK gene on the short arm of chromosome 2 with the EML-4 gene causes an increase in intracellular tyrosine kinase activity and this pathway plays a critical role in cancer pathogenesis.Targeted therapies for EGFR and ALK genes, which have been shown to be important in lung non-small cell cancer, are among the most important developments in this regard.