Sequential Treatment of Afatinib and Osimertinib in Patients with Advanced Non-small Cell Lung Cancer Harboring EGFR Mutations: Results from a Real-world Study in South Korea

The optimal sequence for administration of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) for treating non-small cell lung cancer (NSCLC) is still unclear. This study aimed to evaluate the ecacy of sequential afatinib and osimertinib treatment in patients with NSCLC harboring EGFR mutations. Electronic records of patients with EGFR-mutated NSCLC, who were administered afatinib and osimertinib (group A) or other chemotherapy (group B) between October 2014 and October 2019, across 16 hospitals in South Korea were reviewed. The primary outcome, time on treatment (TOT), secondary outcome, and overall survival (OS) were estimated using the Kaplan-Meier method and log-rank test. Multivariate analyses were performed using the Cox proportional hazards model. Of the 737 patients who received frontline afatinib treatment, 360 with complete records were selected (group A:154, group B: 206). The median TOT was 33.9 months (95% condence interval [CI]: 24.5−43.3) in group A and 21.3 months (95% CI: 19.4−23.1) in group B. The median TOT with afatinib was 12.9 months (95% CI: 11.8−14.0) overall, and 15.2 months (95% CI: 13.2−17.1) in group A. The 2- and 3-year survival rates were 86.0% and 69.3% in group A and 75.9% and 55.3% in group B, respectively. Sequential afatinib and osimertinib treatment resulted in better survival rates than treatment with afatinib followed by other chemotherapies. Therefore, this sequential treatment strategy may offer clinical benets to patients with EGFR-mutated NSCLC.


Introduction
Lung cancer is the leading cause of cancer-related deaths in Korea, accounting for approximately 20% of all cancerrelated deaths; in 2018, 19,317 people died from the disease 1 . Globally, 18.4% of all cancer-related deaths were attributable to lung cancer, and approximately 2 million people were newly diagnosed in 2018 2 .
Afatinib is a second-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) that is suggested as the primary treatment option for progressive, EGFR-mutated NSCLC 3 . A recent head-to-head trial demonstrated that afatinib was superior to ge tinib, a rst-generation TKI, showing better progression-free survival (PFS) and time-to-treatment failure (TTF) 4 . Despite having many advantages over standard platinum-based chemotherapy and rst-generation EGFR TKIs, mutations that confer resistance to afatinib are important clinical problems. The T790M resistance mutation, which is found in exon 20 of the EGFR gene, has been identi ed in approximately 50% of patients receiving afatinib as a rst-line therapy 5 . The AURA study showed a high objective response rate (ORR) and encouraging PFS with the third-generation EGFR TKI, osimertinib, in patients with T790Mmutated NSCLC previously treated with another TKI 6 . Based on studies to date, the expected median period for sequential TKI treatment is approximately 24 months, 13 to 14 months with afatinib and 10 to 13 months with osimertinib 4,6,7 .
Real-world data (RWD) are generally used to monitor post-market safety and adverse events. RWD additionally allow clinical decision-making on patient groups that have been excluded by the generally strict inclusion/exclusion criteria of randomized clinical trials (RCTs). Such patients include elderly patients, those with poor performance status, those harboring uncommon EGFR mutations (i.e., neither the exon 19 deletion [Del19] nor L858R), and those with brain metastases. Thus, RWD may better re ect actual clinical conditions. The GioTag study, a retrospective, observational, and global multicenter study of NSCLC patients who received sequential treatment with afatinib and osimertinib, revealed a median TKI-therapy period of 27.6 months and found that patients with the exon 19 mutation were appropriate candidates for these TKI therapies 8 . In a subgroup analysis of 50 Asian patients, the median time on TKI therapy was ~ 46.7 months. Other RWD from South Korea indicated that the median PFS was 19.1 months for afatinib, 13.7 months for ge tinib, and 14.0 months for erlotinib, respectively 9 .
Several studies have been conducted in Asian populations on the cumulative advantage of frontline treatment with afatinib in a real-world setting in NSCLC patients harboring EGFR mutations [9][10][11][12][13] . However, there is still a paucity of RWD regarding the clinical characteristics and outcomes of patients who were treated sequentially with afatinib and osimertinib. Moreover, considering the controversy on whether osimertinib should be used as rst-line TKI therapy or second-line TKI therapy after failure of rst-or second-generation TKIs, the acquisition of data comparing rst-line afatinib followed by second-line osimertinib with other second-line treatments is warranted. In this context, the present study evaluated the clinical characteristics and treatment outcomes in patients with EGFR-mutated NSCLC who received rst-line treatment with afatinib and second-line therapy with either osimertinib or other regimens by analyzing RWD in South Korea.

Patient characteristics
A total of 737 patients with EGFR-mutated advanced-stage NSCLC were enrolled in the study. Of these, we excluded 367 patients: 164 patients continued afatinib therapy, 110 experienced progressive disease with no available data on second-line treatment, 10 refused treatment, 15 discontinued treatment due to afatinib toxicity, and 68 were transferred or lost to follow-up. A nal set of 360 eligible patients (154 in group A and 206 in group B) were selected.
The study ow chart is depicted in Supplementary Fig. 1. The baseline characteristics of the study participants are summarized in Table 1. The tumor stage was more advanced in group A patients than in group B patients. The latter group experienced a higher percentage of newly appeared or aggravated brain metastases. Other variables were not statistically different between groups A and B. At the start of second-line treatments, the presence and type of brain metastasis were well balanced.

Multivariate Cox PH analysis of factors affecting TOT-1
In all patients, the multivariate Cox PH model revealed that poor ECOG PS, advanced tumor stage, tissue type other than adenocarcinoma, presence of liver metastasis, and no afatinib dose adjustment were related to decreased TOT-1 (Fig. 3). In group A, the hazard ratio (HR) was higher in patients with advanced tumor stage, and the presence of liver metastasis was associated with a marginally signi cant decrease in TOT-1 (Fig. 4).

Multivariate Cox PH analysis of factors affecting TOT-2 in group A patients
In group A patients who received second-line osimertinib treatment, the presence of liver metastasis was associated with a decrease in TOT-2 with an HR of 1.9 (95% CI: 1.13-3.3, P = 0.016, Supplementary Fig. 2).

ORR-1 and DCR-1
The results of ORR-1 and DCR-1 are shown in Supplementary Tables 1 and 2 Table 6). The OS was signi cantly longer in group A than in group B (P = 0.0016, Supplementary Fig. 3).

Discussion
The present study compared the data of patients who received sequential treatment with afatinib and osimertinib to those of patients who received second-line treatments other than osimertinib. We comprehensively investigated clinical outcomes (i.e., TOT, OS, DCR, and ORR) and robustly evaluated the factors affecting TOT in afatinib and osimertinib treatments. Considering the controversies regarding the use of rst-line osimertinib followed by other therapies or rst-line rst-/second-generation TKIs followed by osimertinib as appropriate options for treating EGFRmutated NSCLC patients 15  RWD may differ from RCT data for several reasons. RCTs traditionally require strict criteria for study entry, but this would guarantee unbiased distribution of confounding factors, support causality, and provide strong internal validity; thus, evidence from the RCTs has been considered the gold standard. However, because patients with poor performance status, presence of brain metastasis, advanced age, and comorbidities are seldom included, RCTs may suffer from the loss of clinical diversity. Therefore, the importance of RWD in clinical practice has become apparent.
RWD can provide supplemental data and additional understanding on top of that from RCTs 16 . In particular, concordance between RWD and RCT data could establish the best approach for managing patients.
However, in terms of sequential therapy with afatinib and osimertinib, only a small number of studies have investigated the clinical characteristics and outcomes in patients with EGFR-mutated NSCLC. In the real-world GioTag study 8  During rst-and second-line treatments, the overall TOT in all patients within RESET was 26.4 months. The median TOT in group A patients within RESET was estimated to be 33.9 months, which is slightly shorter than that of Asian patients within GioTag, 46.7 months 8 . However, given that only a small number of Asian patients were included in GioTag, the proportion of elderly patients (≥ 65 years) was higher in RESET (43.9% vs. 34.8%), and RESET included a higher percentage of patients with baseline brain metastasis (43.9% vs. 10.3%) 8 , the results of RESET are encouraging. The RWD from the RESET study is further supported by another multicenter retrospective study in Japanese patients 18 . In this study, patients sequentially treated with afatinib and osimertinib showed better ORR and DCR than patients treated with other rst-generation TKIs (i.e., ge tinib and erlotinib). The above observational studies using RWD highlight the e cacy of sequential treatment with afatinib and osimertinib. RESET assessed several factors affecting TOT-1 using a multivariate Cox PH model. Poor performance status (ECOG PS ≥ 2 vs. 0-1), advanced tumor stage (AJCC 4B vs. 3), tissue type other than adenocarcinoma, liver metastasis, and no afatinib dose adjustment were shown to be related to decreased TOT-1. Interestingly, afatinib dose adjustment was associated with better outcomes for TOT. It is not clear whether TOT was better due to dose reductions, or whether TOT was worse due to dose maintenance, but a study that investigated the effect of dose adjustment on survival outcomes in patients with EGFR-mutated NSCLC reported that patients who received dose reductions experienced higher ORRs 19 . Another RWD study showed that dose adjustment reduced the number and intensity of several side effects, emphasizing that tailored dose modi cation could help treatment optimization and improve survival outcomes 20 . In addition, a post-hoc analysis of LUX-Lung 3 and 6 trials showed that dose reduction was more common in female, old-age, low-weight, and Asian-Japanese patients 21 . Dose reduction led to fewer adverse events and less treatment discontinuation.
Notably, the TOT-1 in group A patients was greater than that in group B patients. Tanaka 23 . Although the mechanism of resistance to EGFR-TKIs might be heterogeneous, the slow growth rate of T790M-harboring cells could partially explain this observation 24 . These ndings might account for the better survival outcomes in patients who developed the T790M mutation after rst-line afatinib treatment, indicating potential association between a longer treatment period and development of the mutation.
Several EGFR-TKIs have been developed to address the problem of EGFR mutations following therapy. Currently, the standard treatment option for patients with EGFR-mutated advanced-stage NSCLC is an EGFR-TKI. Considering its superior e cacy in terms of PFS, OS, central nervous system activity, and adverse events, clinicians prefer osimertinib as rst-line therapy 25 . Despite these bene ts, inevitably acquired mutations during osimertinib therapy, such as the C797S mutation 26 , as well as the interpatient, intratumoral, and intertumoral heterogeneity of NSCLC 27 , complicate the optimal therapeutic determination of EGFR-TKI sequence. The optimal sequence of treatment remains controversial 15 . In particular, in the National Health Insurance of South Korea, osimertinib is only approved for second-line treatment after failure of other rst-line EGFR-TKI treatments. Therefore, sequential treatment of rstor second-generation EGFR-TKIs with the third-generation EGFR-TKI, osimertinib, is a possible alternative.
The RESET study has limitations. First, the main limitation resulted from RESET's retrospective nature. Selection bias or misclassi cation existed. To mitigate this problem, subgroup analyses were performed to identify any potential factors signi cantly affecting survival outcomes. The results of multicenter hospital-based surveillance from RESET could provide insight into the universality of the e cacy of sequential treatment with afatinib and osimertinib. Second, TOT-2 was shorter than TOT-1, which is opposite to the nding in GioTag. TOT-1 in GioTag might have been rather short due to inclusion criteria and drug availability. And also, this may have originated from the short observation period of osimertinib treatment in RESET, in which survival data were not matured at the time of analysis; further data collection and analysis may be warranted. regarding the date and regimen of second-line treatment and new lesions or aggravation of brain metastasis were also collected.

Ethical approval
The study and protocol were approved by the Institutional Review Board (IRB) of the Kosin University Gospel Hospital (KUGH no. 2019-07-038). The study was conducted following the Declaration of Helsinki. All procedures were performed in accordance with the relevant guidelines and regulations. Informed consent was waived due to the retrospective nature of this study, and the approval was gained by the above mentioned IRB.

Outcomes and measurements
The primary outcome was time on treatment (TOT). TOT-1 was de ned as the time from the rst dose of afatinib to tumor progression, TOT-2 was de ned as the time from the rst dose of second-line therapy to tumor progression or death during the treatment, and overall TOT was de ned as the length between the rst dose of afatinib and tumor progression or death during the second-line treatment.
The secondary outcomes were as follows: ( ) ORR-1, de ned as the ratio of total patients who received afatinib to patients experiencing complete remission (CR) or partial remission (PR) after the rst evaluation of tumor response, which was de ned based on Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 14 , (ii) ORR-2 for second-line treatment, (iii) disease control rate-1 (DCR-1), de ned as the ratio of total patients receiving afatinib to patients with CR, PR, and stable disease (SD) after the rst evaluation of tumor response de ned based on RECIST version 1.1, (iv) DCR-2 for osimertinib, and ( ) overall survival (OS), de ned as the length of time from the start of afatinib to death from any cause. Patients still on treatment were censored at the time of data collection.

Statistical analysis
The baseline patient characteristics were descriptive. Chi-squared and Fisher's exact tests were used to compare the differences between categorical variables. TOT and OS were estimated with the Kaplan-Meier method and differences in time distributions were compared using the log-rank test; the estimated median time (months) and