# Osimertinib treatment based on plasma T790M monitoring in patients with EGFR-mutant non-small-cell lung cancer (NSCLC): EORTC Lung Cancer Group 1613 APPLE phase II randomized clinical trial

J. Remon, B. Besse, S. Ponce Aix, A. Callejo, K. Al-Rabi, R. Bernabe, L.

Greillier, M. Majem, N. Reguart, I. Monnet, et al.

► To cite this version:

J. Remon, B. Besse, S. Ponce Aix, A. Callejo, K. Al-Rabi, et al., Osimertinib treatment based on plasma T790M monitoring in patients with EGFR-mutant non-small-cell lung cancer (NSCLC): EORTC Lung Cancer Group 1613 APPLE phase II randomized clinical trial. Annals of Oncology, 2023, 34 (5), pp.468-476. 10.1016/j.annonc.2023.02.012. hal-05036197

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ORIGINAL ARTICLE

# Osimertinib treatment based on plasma T790M monitoring in patients with EGFR-mutant non-small-cell lung cancer (NSCLC): EORTC Lung Cancer Group 1613 APPLE phase II randomized clinical trial

J. Remon<fnref n="1" />, B. Besse<fnref n="1" />, S. Ponce Aix², A. Callejo³, K. Al-Rabi⁴, R. Bernabe⁵, L. Greillier⁶, M. Majem⁷, N. Reguart⁸, I. Monnet⁹, S. Cousin¹⁰, P. Garrido¹¹, G. Robinet¹², R. Garcia Campelo¹³, A. Madroszyk¹⁴, J. Mazières¹⁵, H. Curcio¹⁶, B. Wasąg¹⁷, Y. Pretzenbacher¹⁸, B. Fournier¹⁸, A.-M. C. Dingemans¹⁹ & R. Dziadziuszko¹⁷*

<figure><img src="image_2.png" /></figure>

Available online 28 February 2023

**Background:** The APPLE trial aimed to evaluate the feasibility of longitudinal plasma epidermal growth factor receptor (EGFR) T790M monitoring for the best sequencing strategy of gefitinib and osimertinib.

**Methods:** APPLE is a randomized, non-comparative, phase II study in patients with common EGFR-mutant, treatment-naive non-small-cell lung cancer including three arms: arm A (osimertinib upfront until RECIST progression, PD), arm B [gefitinib until emergence of circulating tumor DNA (ctDNA) EGFR T790M mutation by cobas EGFR test v2 or RECIST PD], and arm C (gefitinib until RECIST PD), and then switch to osimertinib in both arms. The primary endpoint is the progression-free survival (PFS) rate 'on osimertinib' at 18 months (PFSR-OSI-18) after randomization in arm B (H₀: PFSR-OSI-18 of ≤40%). Secondary endpoints include response rate, overall survival (OS), and brain PFS. We report the results of arms B and C.

**Results:** From November 2017 to February 2020, 52 and 51 patients were randomized into arms B and C, respectively. Most patients were females (70%) and had EGFR Del19 (65%); one-third had baseline brain metastases. In arm B, 17% of patients (8/47) switched to osimertinib based on the emergence of ctDNA T790M mutation before RECIST PD, with a median time to molecular PD of 266 days. The study met its primary endpoint of PFSR-OSI-18 of 67.2% (84% confidence interval 56.4% to 75.9%) in arm B versus 53.5% (84% confidence interval 42.3% to 63.5%) in arm C, with a median PFS of 22.0 months versus 20.2 months, respectively. The median OS was not reached in arm B versus 42.8 months in arm C. Median brain PFS in arms B and C was 24.4 and 21.4 months, respectively.

**Conclusions:** The serial monitoring of ctDNA T790M status in advanced EGFR-mutant non-small-cell lung cancer during treatment with first-generation EGFR inhibitors was feasible, and a molecular progression before RECIST PD led to an earlier switch to osimertinib in 17% of patients with satisfactory PFS and OS outcomes.

**Key words:** osimertinib, EGFR-mutant, advanced non-small-cell lung cancer, ctDNA, molecular progression, liquid biopsy

INTRODUCTION

Common activating epidermal growth factor receptor (EGFR) mutations comprise exon 19 deletions (Del19) and exon 21 L858R point mutations in non-small-cell lung cancer

(NSCLC), representing up to 90% of all EGFR mutation subtypes. The incidence of these subtypes is ~40%-60% in Asian patients compared with up to 15% in Western patients with NSCLC.<sup>1,2</sup>

Before 2016, first- or second-generation EGFR tyrosine kinase inhibitors (TKIs) were the standard first-line treatment options for patients with advanced EGFR-mutant NSCLC, given the evidence of response rate (RR) superiority, longer progression-free survival (PFS), and better quality of life compared with platinum-based chemotherapy.<sup>3</sup> Despite

<footnote n="1">¹Paris-Saclay University, Institut Gustave Roussy, Villejuif, France; ²Hospital Universitario 12 De Octubre, Madrid; ³Hospital Universitari Vall d'Hebron-Vall d'Hebron Institut Oncologia, Barcelona, Spain; ⁴King Hussein Cancer Center, Amman, Jordan; ⁵University Hospital Virgen del Rocío, Seville, Spain; ⁶Aix Marseille University, Assistance Publique-Hôpitaux de Marseille (APHM), Marseille, France; ⁷Hospital De La Santa Creu I Sant Pau, Barcelona; ⁸Hospital Clinic Universitari de Barcelona, IDIBAPS, Barcelona, Spain; ⁹Centre Hospitalier Intercommunal De Creteil, Creteil; ¹⁰Institut Bergonie, Bordeaux, France; ¹¹Hospital Universitario Ramon y Cajal, Madrid, Spain; ¹²CHU de Brest, Brest, France; ¹³University Hospital A Coruna-Hospital Teresa Herrera, A Coruna, Spain; ¹⁴Institut Paoli-Calmettes, Marseille; ¹⁵CHU de Toulouse-Hopital Larrey, Toulouse; ¹⁶Centre François Baclesse, CHU Côte de Nacre, Caen, France; ¹⁷Medical University of Gdansk, Gdansk, Poland; ¹⁸EORTC Headquarters, Brussels, Belgium; ¹⁹Erasmus Medical Center, Rotterdam, Netherlands</footnote>

<footnote>*Correspondence to: Prof. Rafal Dziadziuszko, Department of Oncology and Radiotherapy and Early Phase Clinical Trials Center, Medical University of Gdańsk, Gdańsk, Poland
E-mail: rafald@gumed.edu.pl (R. Dziadziuszko).</footnote>

<footnote>0923-7534/© 2023 Published by Elsevier Ltd on behalf of European Society for Medical Oncology.</footnote>
high initial response to EGFR TKIs, acquired resistance occurs within 9 to 15 months after treatment initiation, as a consequence of the *EGFR* T790M mutation in exon 20 in up to 60% of the patients.⁴ Treatment options after the failure of EGFR TKIs such as chemotherapy or EGFR TKIs beyond progression have shown limited RR and PFS.⁵⁻⁷ The development of third-generation EGFR TKIs such as osimertinib, however, offered a new treatment opportunity in this setting. In the phase I AURA trial, osimertinib was associated with an RR of 61% and median PFS of 9.6 months in patients with *EGFR*-mutant advanced NSCLC with radiological progression on previous EGFR TKI in whom T790M-mediated drug resistance had been detected in a new tissue biopsy. The trial also reported some efficacy of the drug in T790M-negative tumors, although the magnitude of the benefit was significantly lower.⁸ Later in 2017, in the treatment-naive cohort from the phase I AURA trial, osimertinib demonstrated a robust RR and prolonged PFS, suggesting that osimertinib was a valuable treatment strategy in the first-line setting,⁹ which was confirmed in 2018 in the phase III FLAURA trial.¹⁰

In daily practice, due to the location or size of the progressive disease, not all patients who start treatment with first- or second-generation EGFR TKIs are suitable candidates for new tissue biopsies at the time of progression, which can delay treatment initiation. Moreover, tumor heterogeneity is a well-recognized issue that makes a single tissue biopsy in a metastatic site not representative of the entire genomic landscape of the tumor at progression.¹¹⁻¹³ Finally, it remains unknown whether the earlier detection of resistance mechanisms and cancer interception may have an impact on patients' outcomes.¹⁴

In this setting, several authors have reported that the assessment of T790M status in circulating tumor DNA (ctDNA) was feasible and predictive for osimertinib efficacy,¹⁵,¹⁶ and some authors have even reported that molecular progression preceded the radiological progression.¹⁷ These data suggest that molecular progression may be a potential approach for making dynamic treatment decisions.

Therefore, in 2015, the European Organization for Research Treatment and Cancer (EORTC) Lung Cancer Group designed a non-comparative clinical trial in the first-line setting for patients with common *EGFR*-mutant NSCLC, aiming to evaluate the feasibility of the assessment of sequential plasma *EGFR* T790M, and the best sequencing strategy for gefitinib and osimertinib therapy (molecular or radiological progression). Here, we report the primary endpoint of the trial.

## METHODS

### Study design

EORTC-1613-APPLE is a randomized, open-label, non-comparative, multicenter, three-arm phase II study in treatment-naive patients with common *EGFR*-mutant advanced NSCLC. Patients were centrally randomized into the following groups: arm A: osimertinib (80 mg daily) until

progression (PD) according to Response Evaluation Criteria In Solid Tumors (RECIST) 1.1 (exploratory arm); arm B: gefitinib (250 mg daily) until the emergence of circulating tumor T790M-positive DNA or PD according to RECIST, whichever came first, then switching to osimertinib until a second PD according to RECIST; or arm C: gefitinib until PD according to RECIST, then switching to osimertinib until a second radiological PD. In all arms, a plasma ctDNA T790M test was carried out centrally using the Cobas *EGFR* mutation test v2 (Roche Molecular Diagnostics Rotkreutz, Switzerland), in parallel with each computed tomography (CT) scan, but was only applied as a predictive marker for making treatment decisions in arm B. All ctDNA analyses were collected, stored, and centrally analyzed at the Medical University of Gdańsk (Poland). Patients were randomized upon the report of adequate sample for the ctDNA *EGFR* T790M test by the central laboratory. Tumor assessments by thoracic and upper abdomen contrast-enhanced CT and brain CT scans were carried out every 8 weeks (±1 week). Brain metastases at baseline (yes or no), *EGFR* mutation subtype (Del19 or L858R), and initial T790M status (yes or no) were stratification factors. All patients had measurable disease as per RECIST v1.1, Eastern Cooperative Oncology Group performance status (ECOG PS) ≤1, and an archival tumor tissue sample. The *EGFR* mutation was carried out by local testing. Complete eligibility criteria are provided in the trial protocol (see Supplementary Materials, available at https://doi.org/10.1016/j.annonc.2023.02.012).

This trial was conducted in accordance with the Declaration of Helsinki and the International Conference on Harmonization Good Clinical Practice Guidelines. The study protocol and amendments were approved by an institutional review board or independent ethics committee at each site. All patients provided written informed consent.

**Endpoints and assessment.** The primary endpoint of the trial was the PFS rate (by RECIST 1.1) while receiving osimertinib at 18 months (PFSR-OSI-18) in arm B. This endpoint was defined as the proportion of patients at 18 months after randomization who were alive and had not experienced an event during treatment with gefitinib or osimertinib (with disease progression according to RECIST 1.1 or death after switching to osimertinib, whichever came first). Although this endpoint was assessed in all arms, it was only formally tested in arm B.

This primary endpoint was chosen with the following assumptions: in arms B and C there were two treatment strategies (sequential approach), whereas in arm A there was only one; we aimed to explore whether patients could be as long as possible on treatment with EGFR TKIs. Therefore, to obtain a homogeneous definition across treatment arms, we adopted PFSR-OSI-18 as the primary endpoint.

Secondary endpoints included PFS, overall RR (ORR), overall survival (OS), and brain PFS (BPFS). The PFS is defined as the time interval between the date of randomization and the date of disease progression according to RECIST 1.1 or the date of death after switching to
osimertinib, whichever comes first. For patients not able to start osimertinib, and for whom the event of interest could not be observed, the date of first disease progression during gefitinib according to RECIST 1.1 was used instead in the definition above. Patients were censored at the date of their last imaging assessment in case no event was observed. The OS is defined as the time interval between the date of randomization and the date of death. The ORR was assessed using RECIST 1.1 criteria. The BPFS was defined as the time interval between the date of randomization and the date of brain progression or death, whichever occurred first.

**Statistical analysis.** The primary analysis was carried out on the per-protocol population (PPP) defined as all eligible patients who started their allocated treatment. The initial sample size, based on a single proportion for the PFSR-OSI-18, was designed to reject a rate of 40% (null hypothesis) in favor of 60% (alternative hypothesis). With type I and type II errors both initially set at 10%, 49 eligible patients per arm were required, and the decision rule to declare arm B feasible was that at least 25 patients should be alive and progression free at 18 months. For this sample size, calculations with EAST software showed that the exact type I error was 8%. Due to some patients failing to meet the eligibility criteria, however, the required number of patients could not be reached. Consequently, the PFSR-OSI-18 was carried out using the Kaplan-Meier technique and its corresponding 84% confidence interval (CI) was used for the decision rule instead. The experimental arm will be considered a success if the lower bound of the two-sided 84% CI is >40% (corresponding to a type I error of 8%).

The ORR to osimertinib was estimated with a 95% CI based on exact binomial distribution and was only assessed in patients who switched to osimertinib. The median time for time-to-event endpoints (PFS, OS, and BPFS) was estimated using the Kaplan-Meier method with two-sided 95% CIs. Hazard ratios and their 95% CIs were estimated based on a Cox proportional-hazards model stratified by the randomization factors. The clinical cut-off date for the present analysis was set at 24 August 2021. Statistical analysis was conducted using SAS 9.4.

## RESULTS

From November 2017 to February 2020, 52 and 51 patients across six countries were randomized to arms B and C, respectively. Table 1 summarizes the population characteristics. In arms B and C, most patients were females (75% and 65%), the median age was 69 and 61 years, the proportion of those who had never smoked was 71% and 59%, and EGFR Del19 was noted in 64% and 65% of tumors, respectively. About one-third of patients had baseline brain metastases. No patients were T790M-positive at baseline. The median sum of the target lesions measurements at baseline was 50 mm in arm B and 53 mm in arm C.

All randomly assigned patients received at least one dose of the trial treatment. At the time of data cut-off, the median duration of gefitinib treatment exposure was 39.9 weeks (range: 3.6-103.0 weeks) for patients in arm B and 40.3 weeks (range: 1.1-124.4 weeks) for patients assigned to arm C. The median duration of osimertinib treatment exposure was 36.1 weeks (range: 3.0-124.9 weeks) for patients in arm B and 28.1 weeks (range: 0.1-132.0 weeks) for patients in arm C. According to eligibility criteria and after medical review, 47 and 44 patients in arms B and C, respectively, were analyzed for efficacy (PPP) (Figure 1). There were 12 excluded patients for whom the inclusion criteria were not met because of: active infection (N = 2), cardiac disorders (N = 2), concurrent treatment (N = 1), laboratory data (N = 2), insufficient delay since prior treatment (N = 1), and other reasons (N = 4).

<table><caption>Table 1. Demographic and clinical characteristics of the patients at baseline</caption><thead><tr><th></th><th>Arm B<br>N = 52</th><th>Arm C<br>N = 51</th></tr></thead><tbody><tr><td>Age</td><td></td><td></td></tr><tr><td>Median, years</td><td>69</td><td>61</td></tr><tr><td>Range</td><td>(31-83)</td><td>(33-89)</td></tr><tr><td>Female sex, n (%)</td><td>39 (75)</td><td>33 (65)</td></tr><tr><td>Race, n (%)</td><td></td><td></td></tr><tr><td>Caucasian</td><td>42 (81)</td><td>38 (74)</td></tr><tr><td>Asian</td><td>1 (2)</td><td>1 (2)</td></tr><tr><td>Black</td><td>0 (0)</td><td>0 (0)</td></tr><tr><td>Other/missing</td><td>9 (14)</td><td>12 (24)</td></tr><tr><td>Smoking status, n (%)</td><td></td><td></td></tr><tr><td>Never</td><td>37 (71)</td><td>30 (59)</td></tr><tr><td>Former</td><td>12 (23)</td><td>17 (33)</td></tr><tr><td>Current</td><td>3 (6)</td><td>3 (6)</td></tr><tr><td>WHO performance status, n (%)</td><td></td><td></td></tr><tr><td>0</td><td>23 (44)</td><td>26 (51)</td></tr><tr><td>1</td><td>28 (54)</td><td>22 (43)</td></tr><tr><td>EGFR mutation, n (%)</td><td></td><td></td></tr><tr><td>Exon 19 deletion</td><td>33 (64)</td><td>33 (65)</td></tr><tr><td>L858R</td><td>19 (36)</td><td>18 (35)</td></tr><tr><td>Median tumor volume (mm)<sup>a</sup></td><td>50</td><td>53</td></tr><tr><td>Brain metastases, n (%)</td><td>16 (31)</td><td>14 (28)</td></tr></tbody></table>

In arms B and C, five and seven patients were considered ineligible after central medical review, respectively. In arm B, the ineligibility criteria were as follows: laboratory data showing low creatinine clearance (n = 1), active infection (n = 1), cardiac disorders involving QTc alterations (n = 1), concomitant drugs not allowed (n = 1), and other (n = 1). In arm C, the ineligibility criteria were as follows: laboratory data showing low creatinine clearance (n = 1), active infection (n = 1), cardiac disorders involving QTc alterations (n = 1), ongoing radiotherapy (n = 1), and others (n = 3).

EGFR, epidermal growth factor receptor.

The ORR and median PFS of gefitinib were 53.2% (95% CI 38.1% to 67.9%) and 10.7 months (95% CI 8.4-17.5 months) in arm B, and 56.8% (95% CI 41.0% to 71.7%) and 9.8 months (95% CI 9.1-12.9 months) in arm C, respectively.

## Switch to osimertinib and RR

In arm B, 32/47 (68%) patients switched to osimertinib, with 8/47 (17%) switching due to the emergence of a T790M mutation in ctDNA analysis (molecular progression) and 24/47 (51%) due to RECIST progression without T790M mutation detected in ctDNA. In the remaining 15 patients who did not switch, 4 were still being treated with gefitinib at the time of the clinical cut-off date and the other 11 patients had stopped protocol treatment without starting

<footnote>aMedian sum of tumor diameters based on target lesions.</footnote>
<figure><img src="image_3.png" /><figcaption>**Figure 1.** Trial profile.

ctDNA, circulating tumor DNA; PD, progressive disease; PPP, per-protocol population.</figcaption></figure>

osimertinib due to the progression of disease (3/11), toxicity (4/11), patient's decision (1/11), and other reasons (3/11). Among the eight patients with molecular progression, the median time elapsed between gefitinib initiation and ctDNA T790M positivity was 266 days (56-672 days).

In arm C, 34/44 (77%) started osimertinib, 2 were still on gefitinib, and 8 patients were not able to start osimertinib due to the progression of disease (1/8), toxicity (4/8), investigator's decision (2/8), and death not due to malignant disease or toxicity (1/8) (Figure 2).

The ORR to osimertinib was 65.6% (95% CI 46.8% to 81.4%) in arm B and 58.8% (95% CI 40.7% to 75.4%) in arm C (P = 0.5692). In arm B, the ORR to osimertinib was 87.5% (95% CI 47.3% to 99.7%) for patients switching based on molecular progression and 58.3% (95% CI 36.6% to 77.9%) for the 24 patients switching based on radiological progression. Only 1 out of these 24 patients had a molecular progression at the time of osimertinib initiation. In arm C, the T790M status at the time of RECIST PD was blinded for making treatment decisions. In arm C, at the time of RECIST PD allowing for osimertinib initiation, however, seven

<figure><img src="image_4.png" /><figcaption>**Figure 2.** Summary of subsequent osimertinib in patients in arms B and C, including those in arm B who switched based on molecular progression (ctDNA T790M-positive) and those who switched based on radiological progression by RECIST 1.1 criteria.</figcaption></figure>

In arm B, 8/47 (17%) of the per-protocol population switched to osimertinib, based on ctDNA T790M positivity.
ctDNA, circulating tumor DNA.
patients had a concomitant T790M positivity in the ctDNA analysis.

## PFSR and OS

After a median follow-up of 30 months, in arm B (n = 47), the PFSR-OSI-18 was 67.2% (84% CI 56.4% to 75.9%), representing the success for this strategy, as the lower bound of the CI was >40%. In arm B, the PFSR-OSI-18 according to

the osimertinib switch criteria was 87.5% (84% CI 38.7% to 98.1%) for patients who switched to osimertinib based on molecular progression (8/32), whereas it was 62.5% (84% CI 40.5% to 78.4%) for those who switched to osimertinib based on RECIST PD (24/32). The median PFS was 22.1 months [95% CI 21.9 months-not reached (NR)] and 21.9 months (95% CI 16.6 months-NR), respectively. In arm C (n = 44), the PFSR-OSI-18 was 53.5% (84% CI 42.3% to 63.5%).

<figure><img src="image_5.png" /><figcaption>Figure 3. (A) Progression-free survival at 18 months in arms B and C. (B) Subgroup analysis of progression-free survival in arms B and C.</figcaption></figure>

CI, confidence interval; df, degrees of freedom; EGFR, epidermal growth factor receptor; HR, hazard ratio; KM est, Kaplan-Meier estimat; NR, not reached; Osi, osimertinib.

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>
<figure><img src="image_8.png" /><figcaption>**Figure 4. Overall survival.**</figcaption></figure>

CI, confidence interval; KM est, Kaplan-Meier estimate; NR, not reached; O, number of events observed.

An exploratory comparison of median PFS in arms B and C was carried out. The median PFS was 22.0 months (95% CI 18.6 months-NR) and 20.2 months (95% CI 14.6-35.0 months), and the hazard ratio was 0.80 (90% CI 0.51-1.27; *P* = 0.22) (Figure 3A). In the exploratory subgroup analysis across all predefined subgroups (Figure 3B) including the EGFR mutation subtype and the presence of CNS metastases at trial entry, there was no subgroup with a significant difference between arms B and C.

The median OS was not reached in arm B and was 42.8 months (95% CI 27.0 months-NR) in arm C, with an 18-month OS probability of 87% (84% CI 78.1% to 92.5%) and 77.3% (84% CI 66.9% to 84.8%), respectively (Figure 4). In both arms, 17 patients died, with progression of the disease as the main reason for death.

The median BPFS in arms B and C was 24.4 months (95% CI 17.9-28.6 months) and 21.4 months (95% CI 14.5-42.8 months; hazard ratio 1.05; 90% CI 0.65-1.69; *P* = 0.57), respectively (Figure 5).

<figure><img src="image_9.png" /><figcaption>**Figure 5. Brain-progression free survival in arms B and C.**</figcaption></figure>

CI, confidence interval; HR, hazard ratio; Osi, osimertinib.
<table><caption>Table 2. Overall summary of adverse events</caption><thead><tr><th>N, (%)</th><th>Arm B</th><th>Arm C</th></tr><tr><th>During gefitinib treatment<br>(N = patients starting treatment)</th><th>N = 52</th><th>N = 51</th></tr></thead><tbody><tr><td>At least one grade ≥1 AE</td><td>51 (98)</td><td>50 (95)</td></tr><tr><td>At least one grade ≥3 AE</td><td>19 (36.5)</td><td>21 (41.2)</td></tr><tr><td>At least one grade ≥1 TRAE</td><td>46 (88.5)</td><td>43 (84.3)</td></tr><tr><td>At least one grade ≥3 TRAE</td><td>10 (19.2)</td><td>7 (13.7)</td></tr><tr><td>Most common grade ≥1 TRAE</td><td></td><td></td></tr><tr><td>Diarrhea</td><td>27 (51.9)</td><td>21 (41.2)</td></tr><tr><td>Dry skin</td><td>15 (28.8)</td><td>15 (29.4)</td></tr><tr><td>Rash acneiform</td><td>22 (42.3)</td><td>14 (27.5)</td></tr><tr><th>During osimertinib treatment<br>(N = patients starting treatment)</th><th>N = 32</th><th>N = 34</th></tr><tr><td>At least one grade ≥1 AE</td><td>32 (91.4)</td><td>32 (88.9)</td></tr><tr><td>At least one grade ≥3 AE</td><td>9 (25.7)</td><td>11 (30.6)</td></tr><tr><td>At least one grade ≥1 TRAE</td><td>24 (68.6)</td><td>19 (52.8)</td></tr><tr><td>At least one grade ≥3 TRAE</td><td>3 (8.6)</td><td>2 (5.6)</td></tr><tr><td>Most common grade ≥1 TRAE</td><td></td><td></td></tr><tr><td>Diarrhea</td><td>10 (28.6)</td><td>7 (19.4)</td></tr><tr><td>Dry skin</td><td>5 (14.3)</td><td>4 (11.1)</td></tr><tr><td>Rash acneiform</td><td>4 (11.4)</td><td>3 (8.3)</td></tr></tbody></table>

AE, adverse event; TRAE, treatment-related adverse events as per local investigator assessment.

**Safety.** In arm B, 98% of patients experienced adverse events (AEs), including 88% of treatment-related AEs (TRAES) (Table 2). Grade 3 or higher TRAES were noted in 19% of patients, diarrhea being the most common. During osimertinib treatment in arm B, the AEs and TRAESs of grade ≥3 occurred in 91% and 9% of patients, respectively.

The proportion of patients who stopped treatment due to toxicity was 10% in both arms B and C during gefitinib therapy. There was no treatment discontinuation due to toxicity during osimertinib treatment. Osimertinib dose reductions occurred in 10% of patients in arm B and no patients in arm C.

## DISCUSSION

The APPLE trial is the first prospective study in NSCLC to demonstrate the feasibility of using adaptative strategies based on ctDNA for making treatment decisions. The results support that the serial monitoring of ctDNA T790M status is feasible in patients with EGFR-mutant advanced NSCLC for switching to osimertinib. This strategy identified 17% of patients with molecular progression before RECIST PD, leading to an earlier switch to osimertinib with a clinically meaningful 18-month PFS of 67%. At the time of the APPLE trial initiation the Cobas EGFR mutation test v2 was the unique approved plasma-based companion diagnostic for patients for whom osimertinib treatment was indicated as a sequential strategy. It has already been reported that the sensitivity for the detection of plasma-derived T790M is lower with the Cobas plasma test (51%) than with other techniques, such as digital droplet PCR (58%) and next-generation sequencing (66%).¹⁸,¹⁹ Indeed, each platform has a different analytic limit of detection, which can be influenced by the tumor ctDNA shedding capacity, correlated with the baseline lesion size of the tumor target.¹⁸ It

should be noted, however, that if up to 60% of patients develop acquired T790M at the time of RECIST progression, our strategy identified one-third of these patients in advance, allowing for an earlier switch to osimertinib. Indeed, a more sensitive technique for T790M status assessment would likely have increased the proportion of patients undergoing an earlier switch to osimertinib positively impacting the outcomes.

Similarly, one challenging clinical question is whether molecular monitoring and adaptative treatment strategies regardless of radiological status by RECIST may positively impact patients' outcomes compared with the classical approach based on radiological progression.¹⁴ In this scenario, the APPLE trial suggests that an early switch based on molecular progression may have a positive impact on the outcome of these patients, with 67% of patients alive and without RECIST progression at 18 months, which appears better than other previous strategies reporting an 18-month PFS <60%.¹⁰ The satisfactory outcomes of the trial cannot be explained by an overselected population in arm B. The median sum of the longest tumor diameters at baseline in arm B was 50 mm, and it has been reported that larger tumors (>50 mm) were associated with the inferior PFS of first-line EGFR-TKI therapy,²⁰ and 31% of patients had brain metastases at presentation. Although formal comparison between arms B and C reported a numerically improved 18-month PFS in arm B versus C (P = 0.22), the trial was not sufficiently powered for such a comparison, and arm C was underestimated based on our initial criteria of an 18-month PFS of 40%, reaching 53.5%.

It is still being debated whether the sequential treatment approach may have any role in the therapeutic strategy of patients with EGFR-mutant advanced NSCLC. Despite the limitation of the exercise of cross-trial comparisons, the median survival reached in arms B and C of the APPLE trial (median OS: NR and 43 months, 18-month OS: 87% and 77%, respectively) appears impressive compared with survival indices reported in other studies, such as the FLAURA trial (regardless of the treatment arm),²¹ and particularly, with real-world data.²² This is relevant as in the APPLE trial, most of the patients were from Caucasian ethnicity and had poorer prognosis with up to one-third of patients with baseline brain metastases compared with 23% in the FLAURA trial.¹⁰ This benefit in the outcome in the APPLE trial, however, could be driven as a consequence of at least 70% of patients switched to sequential osimertinib at the time of molecular or radiological progression including only 16% of patients (8/58: 1/24 patients in arm B and 7/34 patients in arm C) with T790M-positive ctDNA at the time of RECIST PD. In contrast, in the FLAURA trial only 47% of patients in the control arm received osimertinib at progression according to T790M positivity (31% of all patients initially randomized in the comparator arm of the trial). These data may support, as has been proposed in other oncogenic-driven NSCLC like ALK-positive tumors, that the survival benefit in oncogenic-addicted NSCLC is mainly driven by the access to subsequent personalized approaches rather than simply a delay of disease progression
with a more potent drug upfront.²³,²⁴ Although the APPLE trial included a third arm enrolling patients on osimertinib upfront (arm A), this arm was exploratory at the time of the trial initiation, not allowing formal comparisons, and the results of this arm are still pending. Another potential reason against the use of the sequential therapeutic approach is the risk that patients do not receive any treatment at the time of progression. In the APPLE trial, 23% and 18% of patients per protocol in arms B and C, respectively, did not receive any subsequent treatment. Although this percentage may seem high, it mirrors the ~30% of patients who did not receive subsequent treatment in the FLAURA trial, either in the osimertinib arm or in the comparator arm.²¹

The major limitations of our trial are that the treatment landscape of EGFR-mutant NSCLC has rapidly evolved since the trial was designed, and osimertinib is currently considered as a preferable first-line treatment option by most physicians.²⁵ The trial was designed before this change, however, focusing on the sequential approach (according to the most updated guidelines, this strategy is still considered as an alternative approach in first-line setting),²⁵ and we already included the exclusive osimertinib arm in the design of the APPLE study. Other limitations are the small sample size in the trial subgroups and the relatively low sensitivity of the applied ctDNA test. More sensitive techniques would positively impact on detection rate; however, we had to rely on the test which was approved for clinical use at the time of trial initiation. Despite these limitations, the APPLE trial supports the longitudinal ctDNA assessment as a relevant tool for making treatment decisions, not only for adapting treatment strategies but also for the assessments of escalating or de-escalating treatment in patients with NSCLC.²⁶ In this last scenario, the baseline ctDNA status may help to detect patients with EGFR-mutant NSCLC with worse prognosis. In the FLAURA trial and other trials, it has been reported that the presence of baseline ctDNA associates with worse outcome on EGFR TKIs,²⁷ potentially due to patients having lower tumor burden. The clinical benefits of this strategy must be balanced with the cost and accessibility of longitudinal ctDNA analyses, however, which may limit the implementation of this strategy. In conclusion, the APPLE trial is the first prospective study supporting the role of dynamic adaptive strategies based on ctDNA monitoring in patients with EGFR-mutant advanced NSCLC.

## ACKNOWLEDGEMENTS

The authors would like to acknowledge the support of the EORTC 1613 study team, EORTC Lung Cancer Group members, and Central Laboratory at the Medical University of Gdańsk.

## FUNDING

This work was supported by an educational grant from AstraZeneca (no grant number).

## DISCLOSURE

JR: none directly related to this manuscript. Advisory/speaker: Merck Sharp & Dohme (MSD), Sanofi, Boehringer Ingelheim, Pfizer, Ose Immunotherapeutics, Janssen, and Takeda. Speaker at a company's organized public event: MSD, Boehringer Ingelheim, Roche, and Janssen. Receipt of grants/research support: MSD (principal investigator in PECATI trial).

BB: none directly related to this manuscript. Grant to institution: 4D Pharma, AbbVie, Amgen, Aptitude Health, AstraZeneca, BeiGene, Blueprint Medicines, Boehringer Ingelheim, Celgene, Cergentis, Chugai Pharmaceutical, Cristal Therapeutics, Daiichi-Sankyo, Eli Lilly, Eisai, Genzyme Corporation, GlaxoSmithKline, Inivata, Ipsen, Janssen, Onxeo, OSE Immunotherapeutics, Pfizer, Roche-Genentech, Sanofi, Takeda, Tolero Pharmaceuticals, and Turning Point Therapeutics.

RD: honoraria for consultancy or lectures: AstraZeneca, Roche, Novartis, MSD, Takeda, Pfizer, Amgen, and Bristol-Myers Squibb.

All other authors have declared no conflicts of interest.

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