Non-small cell lung cancer harboring EGFR G724S mutation and exon 19 deletion responded to afatinib monotherapy after multiple lines of target therapies.

Epidermal growth factor receptor (EGFR) G724S mutation represents a resistance mechanism to first- and third-generation EGFR tyrosine kinase inhibitors. Limited data are available regarding the efficacy of afatinib in patients with non-small cell lung cancer (NSCLC) harboring G724S mutation, particularly after osimertinib. A patient diagnosed with advanced EGFR-mutated (exon 19 deletion) NSCLC after several lines of treatment - gefitinib, osimertinib, heat shock protein inhibitors and chemotherapy-developed EGFR G724S mutation retaining the exon 19 deletion. She was then treated successfully with afatinib leading to a progression free survival of 9 months (and counting). This is the first report of the emergence of G724S mutation, together with ex19del, after three subsequent lines of therapy following progressive disease to Osimertinib, and we report for the first time the activity of afatinib against EGFR exon 18 G724S mutation in this setting.

Introduction

We report the case of a patient diagnosed with advanced epidermal growth factor receptor (EGFR)-mutated (exon 19 deletion) non-small cell lung cancer (NSCLC) who, after several lines of treatment developed EGFR G724S mutation, was treated successfully with afatinib.

Case presentation

In November 2012, a 55-year-old never-smoker Caucasian female was diagnosed with stage IV papillary adenocarcinoma – multiple bilateral lung nodules and mediastinal lymph nodes. The patient was staged with total body PET and brain computed tomography (CT) scan. She presented in good clinical conditions, and Eastern Cooperative Oncology Group performance status (PS) is 0. She referred neither any clinically significant symptoms nor relevant comorbidities. Activating EGFR exon 19 deletion (ex19del) E746_S752>V was identified by PCR on tissue biopsy. Thus, in December 2012, the patient was started on first-generation tyrosine kinase inhibitor gefitinib 250 mg daily. In April 2015, the CT scan showed new bilateral lung nodules. A second tissue biopsy and PCR were performed showing both ex19del and EGFR exon 20 T790M mutation. The patient was then treated with four cycles of carboplatin (area under the plasma concentration-time curve 5 mg/ml per min, intravenously, on day 1 every 3 weeks) and pemetrexed (500 mg/m2 intravenously on day 1 every 3 weeks). Then the patient was followed up until June 2016 when she developed new lung nodules. At that time, she was referred to our Institution, and she was started on osimertinib 80 mg daily, within the open-label, single-arm, real-world treatment study ASTRIS [1]. The best response to osimertinib was partial response (PR) according to RECIST criteria v1.1 [2]. In October 2017, she developed progressive disease (PD) with new lung nodules. The tissue biopsy performed at that time showed no T790M and confirmed the presence of the baseline ex19del. Papillary adenocarcinoma histology was also confirmed. Osimertinib was continued beyond progression until February 2018 when the CT scan revealed a further PD, and the patient was treated within a clinical trial (NCT02965885) with TAS-116. TAS-116 is an orally available selective inhibitor of Heat Shock Protein 90 (HSP90). HSPs mediate key signaling pathways for tumor survival, and EGFR levels have been shown to decline upon treatment with HSP90 inhibitors [3]. The disease was controlled until March 2019 when it progressed with new lung nodules. Next-generation sequencing (NGS) through the oncomine focus assay (ThermoFisher Scientific, Waltham, Massachusetts) on tissue biopsy was performed: baseline ex19del was still present, whereas no other molecular alterations were found. The patient was still PS 0 and her only complaint was dyspnea after strenuous exercise. She was subsequently treated with gefitinib 250 mg daily (from March 2019 to November 2019, the best response was PD for pleural effusion) and single-agent gemcitabine (from December 2019 to July 2020). Gemcitabine was suspended with stable disease, due to suboptimal tolerance, and the patient was followed up with CT scans every 3 months. In June 2021, the restaging CT scan showed an increase in the lung nodules. NGS (Oncomine Focus Assay - ThermoFisher Scientific) on tissue biopsy highlighted the ex19del and the emergence of the EGFR exon 18 G724S mutation; neither T790M nor other mutations were found. The case was discussed at the local molecular tumor board, and treatment with afatinib was started in August 2021, in light of the preclinical evidence of sensitivity to afatinib retained by NSCLC harboring exon 18 G724S mutation4. The first restaging CT scan showed that PR and treatment with afatinib are still ongoing. The last CT scan, performed in April 2022, confirmed PR leading to a progression free survival (PFS) of 9 months (and counting). The patient is in good clinical condition, PS is 0 and her current survival, calculated from metastatic cancer diagnosis, is 9.5 years (Fig.1).

Fig. 1

Disease response to afatinib treatment (a) and sequence of treatment received in relation to the emergence of resistance mechanisms (b).

Discussion

In-vitro and in-vivo experiments showed how G724S promotes a conformational change in the EGFR glycine-rich loop inducing resistance, in the context of ex19del, by reducing the binding affinity of osimertinib [4]. The emergence of EGFR exon 18 G724S mutation as a resistance mechanism to osimertinib in patients with NSCLC, and the activity of afatinib in this setting, have already been reported [5,6]. However, to the best of our knowledge, this is the first report of the emergence of G724S mutation, together with ex19del, after three subsequent lines of therapy following PD to Osimertinib. More importantly, we reported for the first time the activity of afatinib against EGFR exon 18 G724S mutation in a later line of treatment. The occurrence of G724S mutation in NSCLC with baseline E746_S752>V ex19del is consistent with what has been observed in previous studies [5]. The patient responded extraordinarily well to anticancer treatments, as shown by the PFS achieved with first-line gefitinib and with chemotherapy both in second and fifth lines [7]. Nonetheless, the disease control achieved with target treatments was in line with the literature and the best response to gefitinib rechallenge was PD [8,9]. This validates the remarkable disease control provided by afatinib, being mechanistically explained by the presence of ex19de/G724S comutation. Our findings are particularly relevant in light of the increasing number of patients receiving osimertinib in first line and the consequent need to tackle resistance mechanisms in subsequent lines of treatment. Real-word experiences are of great value for gathering evidence about the best treatment choice in specific and rare molecular population – such patients with NSCLC harboring the EGFR ex19del/G724S comutation - since developing a specific clinical trial would not be feasible. Furthermore, our case highlights the value of genotyping oncogene-addicted NSCLC, even in later lines of treatment, in order to deliver the next best treatment. At the same time, it shows how chemotherapy might play a key role in prolonging survival, working as a bridge between target therapies.

Conclusion

We confirmed the efficacy of afatinib monotherapy in patients with NSCLC harboring EGFR ex19del/G724S comutation, gathering evidence for afatinib as the best treatment choice in this very specific patient population.

Acknowledgements

Conflicts of interest

There are no conflicts of interest.