Introduction

Lung cancer is ranked as the most common cause of cancer-related death worldwide. Non-small cell lung cancers (NSCLCs) are currently the most prevalent form, accounting for approximately 80–85% of all lung cancer cases [1]. The majority of patients diagnosed with lung adenocarcinoma are often in advanced stages (stage IV) and derive modest benefit from nonselective cytotoxic chemotherapy [2]. However, the discovery of epidermal growth factor receptor (EGFR) mutations in 2004 has revolutionized the treatment of these patients [3]. Patients with NSCLC with an activating mutation within the epidermal growth factor receptor (EGFR) exhibit a dramatic response to EGFR-tyrosine kinase inhibitors (EGFR-TKIs) [4]. 80–90% of activated EGFR mutations are normally located in exon 19 deletions and L858R substitution in exon 21 [5]. in addition to these known common mutations, there are other remaining rare mutations whose predictive value is still unclear. Some of these are expressed by the coexistence of two common or rare and common mutations together on different exons in the EGFR gene, which are called “compound mutations.” The clinical response of patients with compound EGFR mutations to EGFR‑TKIs remains unclear. Several studies indicate that individuals with compound EGFR mutations may show reduced responsiveness to TKI therapies compared with those with single mutations [6,7,8,9]. Additionally, different treatment efficacies have been associated with different types of EGFR compound mutations [10, 11]. While first-generation EGFR-TKIs could be a useful treatment option, recent studies suggest considering afatinib and osimertinib for patients with compound EGFR mutations, depending on their specific cases [12, 13]. These alternative therapies require further investigation to understand their effectiveness and optimal application in the specific context of patients with compound EGFR mutations.

We present a case report of a patient with common L858R (exon 21) and rare S768I (exon 20) mutations treated with afatinib.

Case report

In April 2017, a 64-year-old male of Moroccan descent, a lifelong nonsmoker with no significant medical or family history, presented with a persistent productive cough accompanied by scant hemoptysis and grade 2 dyspnea, which had been ongoing for 3 months. These symptoms were part of a broader clinical picture marked by a progressive decline in his general health status. A comprehensive evaluation, including a chest computed tomography (CT) scan, unveiled a primary tumor mass measuring 95 mm × 69 mm × 66 mm in the lower right lobe of the lung. Additionally, the imaging indicated the presence of lymphangitic carcinomatosis and lymph node involvement on both the ipsilateral and contralateral sides of the thorax, classifying the disease as T4N3M0 according to the TNM staging system (stage IIIc). To establish a definitive histological diagnosis, a transbronchial lung biopsy was performed on the affected right lobe. Subsequently, formalin-fixed paraffin-embedded tissue sections, measuring 4 μm in thickness, were subjected to hematoxylin and eosin saffron (HES) staining, revealing the presence of acinar lung adenocarcinoma. Immunohistochemical staining confirmed the diagnosis, as it exhibited positivity for cytokeratin 7 (CK7) and transcription factor-1 protein (TTF1). The initial therapeutic approach involved first-line chemotherapy, combining cisplatin at a dosage of 75 mg/m2 with navelbine at 25 mg/m2. Early assessment via CT imaging, performed after the treatment period from 23/11/2017 to 22/12/2017, demonstrated a notable regression in tumor size (from 66 mm × 69 mm × 95 mm to 35 mm × 35 mm × 60 mm) following the initial courses of chemotherapy. However, subsequent CT scans after two cycles of treatment indicated the presence of lung and lymph node metastases, prompting a shift toward palliative chemotherapy. Following this transition, genetic profiling was conducted at the Department of Biomolecular CHU Hassan II to guide personalized therapeutic decisions. DNA extraction was performed from the available histological specimen using the QIAamp DNA FFPE Tissue Kit (Invitrogen), following the manufacturer’s protocols. Genetic analysis employed reverse transcription-polymerase chain reaction (RT-PCR) technology, with the quantitative PCR analysis utilizing the therascreen EGFR RGQ PCR Kit. This analysis revealed the presence of an activating co-mutant involving the L858R mutation in exon 21 (c.2573T>G) and the S768I mutation in exon 20 (c.2303G>T, p.S768I). These mutations were subsequently confirmed through SANGER sequencing (Figs. 1, 2). In April 2018, the patient was administered oral afatinib at a daily dose of 40 mg. A follow-up CT scan conducted 3 months post-initiation of afatinib treatment demonstrated a dramatic reduction in tumor size (Fig. 3), accompanied by a significant amelioration of symptoms such as dyspnea, cough, and hemoptysis. Remarkably, the patient exhibited excellent tolerance to afatinib therapy, facilitating a consistent improvement and a relatively slow progression rate of the disease. This response led to a period of disease stabilization until the detection of bone metastases in December 2020. Subsequent months witnessed a state of relative stability in the progression of the primary tumor and associated nodules, until the emergence of a brain metastasis in April 2021. At this juncture, deliberations surrounding potential stereotactic radiotherapy were undertaken; however, the patient opted against surgical intervention. Regrettably, as of the latest available update on 15 August 2022, we have received information confirming the patient’s death.

Fig. 1
figure 1

Electropherogram traces of exon 20 S768I positive mutation confirmed by Sanger sequencing

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Fig. 2
figure 2

Electropherogram traces of exon 21 L858R positive mutation confirmed by Sanger sequencing

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Fig. 3
figure 3

CT scan results showing the primary tumor in the right lower lobe of the lung before treatment (a), and the dramatic response 3 months post-afatinib treatment (b). The red circle represents the primary tumor before and after treatment

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Discussion

The management of non-small cell lung cancer (NSCLC) has evolved significantly with a focus on identifying driver mutations, such as EGFR and ALK-EML4, within tumor samples to guide personalized treatment strategies. The epidermal growth factor receptor (EGFR) is a member of the ErbB family of receptor tyrosine kinases (RTK) [14]. In NSCLC, mutations in the intracellular region of EGFR have been observed in a range of 43–89% of cases [15]. Among these mutations, more than 90% are accounted for by EGFR TKI-sensitizing mutations, primarily involving exon 19 deletions and the exon 21 L858R substitution [16]. Notably, patients with tumors bearing these activating mutations typically exhibit substantial clinical and radiographic responses to EGFR tyrosine kinase inhibitors (TKIs) such as gefitinib, erlotinib, and afatinib [16].

In contrast, the S768I exon 20 substitution (serine replacing isoleucine at codon 768) is described as a rare mutation, representing ~ 1% of cases [17]. The rarity of S768I mutations has posed challenges in defining their role as molecular predictors of TKI response. However, recent studies have shed light on the clinical significance of S768I mutations in lung adenocarcinoma, demonstrating favorable responses to TKIs [18, 19].

Even rarer than the S768I substitution are compound mutations, which encompass not only single exon mutations, but also combinations of double mutations occurring across different exons of the EGFR gene. These compound mutations often involve a mix of common and rare mutations (Table 1). In our specific case, the compound mutation was identified as a co-occurrence of L858R exon 21 substitution and the exon 20 S768I mutation. This observation may be attributed to the genetic heterogeneity within EGFR mutation-positive non-small-cell lung cancer, leading to clonal evolution and the emergence of diverse molecular characteristics at the cellular level [20].

Table 1 Clinical case summaries—insights from the literature
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Recent studies have highlighted the complexity and heterogeneity of EGFR mutations in NSCLC tumors [20], raising questions about their implications for treatment efficacy. The frequency and response patterns of patients harboring complex mutations remain incompletely defined, primarily due to the limited number of different complex mutations. Generally, compound mutations involving frequent mutations demonstrate similar or improved sensitivity to EGFR-TKI therapy [9], and complex mutations, which combine frequent and sparse mutations (non-resistant), tend to exhibit comparable clinical responses to those associated with frequent mutations alone [21].

The L858R substitution emerges as the most prevalent mutation found in conjunction with other rare mutations [21, 22]. Several studies have emphasized the importance of specific compound mutations. For instance, patients with concomitant L858R and V834L or G873E mutations have demonstrated sensitivity to EGFR-TKIs comparable to those with single L858R mutations [22]. Additionally, the concomitant del-19 + L858R mutation has been associated with a more favorable clinical response to EGFR-TKIs [5].

However, the presence of compound mutations, such as L858R and S768I, in patients with NSCLC presents distinct clinical challenges. Multiple studies have consistently shown that patients with compound EGFR mutations tend to exhibit reduced sensitivity to TKI therapies compared with those with single EGFR mutations [6, 7, 23, 24]. Furthermore, emerging evidence suggests that the specific types of compound EGFR mutations may be linked to different treatment response patterns [11].

Moreover, the S768I mutation has been associated with resistance to first-generation EGFR-TKIs, such as gefitinib and erlotinib, which are commonly used for EGFR-mutated NSCLC [25,26,27]. In response to the intrinsic resistance displayed by the S768I mutation toward first-generation EGFR-TKIs, extensive efforts have been dedicated to exploring alternative therapeutic approaches. Second- and third-generation TKIs, including afatinib and osimertinib, have emerged as promising options, exhibiting notable efficacy against the S768I mutation [25, 28,29,30]. These agents demonstrate a selective binding affinity for the mutant EGFR, effectively surmounting the resistance mechanisms associated with the S768I alteration, thus providing a viable treatment avenue for patients harboring this specific co-mutation.

In the present report, we investigate the efficacy of afatinib EGFR-TKI in the context of a 64-year-old Moroccan male patient who was a lifelong nonsmoker and presented with concomitant L858R and S768I mutations. Remarkably, this patient exhibited an overall survival (OS) of 51 months and a median progression-free survival (PFS) exceeding 39 months following afatinib therapy. These outcomes significantly surpass those reported by Ling et al. [21], who observed a PFS of 6 months and an OS of 6.5 months in a 70-year-old male smoker (20 pack-years) with L858R + S768I complex mutation treated with gefitinib. This intriguing disparity suggests that the S768I + L858R co-mutation may enhance the interaction between EGFR and afatinib compared with gefitinib, resulting in a remarkable clinical response to afatinib TKIs.

Conclusion

EGFR mutation heterogeneity encompasses compound mutations, constituting a distinctive subgroup of patients with NSCLC with varying responses to EGFR tyrosine kinase inhibitors. The present report delineates a rare case of acinar lung adenocarcinoma harboring an L858R point mutation in exon 21 and a compound S768I EGFR substitution mutation. Following treatment with afatinib, this patient demonstrated a highly favorable therapeutic response exceeding 38 months. These findings underscore the complexity of EGFR mutations in NSCLC and emphasize the need for tailored treatment strategies to address the diversity of mutational profiles encountered in clinical practice.