1 Introduction

The anaplastic lymphoma kinase (ALK) gene fusion accounts for about 3–6% of non-small cell lung cancer (NSCLC), which is the second identified targetable driver gene followed by epidermal growth factor receptor (EGFR) mutations in NSCLC [1]. It usually occurs in young, nonsmoking patients with lung adenocarcinoma [2]. At present, according to the National Comprehensive Cancer Network (NCCN) guidelines, the second-generation ALK-tyrosine kinase inhibitors (TKIs), alectinib and brigatinib, and the third-generation ALK-TKI, lorlatinib, are the preferred first-line treatment recommendations for advanced NSCLC patients with ALK gene rearrangements [3]. In clinical practices, patients who simultaneously undergo double ALK fusion are rare, and the fused genes are also diverse [4,5,6,7,8,9,10]. In this report, we present for the first time an unreported case of lung adenocarcinoma with double ALK fusions of echinoderm microtubule-associated protein like 4 (EML4) and histone methyltransferase (SETD2), which is sensitive to alectinib. When the drug resistance to AKI-TKIs occurred, the next-generation sequencing (NGS) test showed that double ALK fusions disappeared. Subsequent immunotherapy combined with chemotherapy is effective and achieves long-term survival benefit.

2 Case presentation

A 28-year-old male with no smoking history presented to the hospital with a persistent cough for half a month in August 2018. Chest computed tomography (CT) scan revealed left upper lobe bronchial stenosis, enlarged multiple mediastinal (2R, 5, 6, 7 zones) and left hilar lymph nodes with multiple nodules in both lungs, left pleural thickening with bilateral pleural and pericardial effusions. And multiple nodular high-density shadows were seen in the left 3rd and 8th ribs, sternum, C1, 7, 11, 12, and the left adnexa of C1. Central type carcinoma of left lung with intrapulmonary, pleural and bone metastasis was considered. Endoscopic biopsy of the left pleural tissue suggested lung adenocarcinoma with ALK-Ventana D5F3, keratin 7, napsin A and thyroid transcription factor-1 (TTF-1) positivity, and adenocarcinoma cells were also found in pleural effusion and pericardial effusion. And EML4-ALK (E14:A21, allelic frequency: 14.05%) and SETD2-ALK (S12:A21, allelic frequency: 25.20%) double-fusion (Fig. 1) were found in the pleural tissue by DNA-based NGS, which can capture all exons of 31 genes that are highly related to the occurrence and development of cancer, and important exons and partial introns of 137 genes that are related to individualized treatment or high frequency mutation of lung cancer, and perform high-depth sequencing up to 1000X. (Burning Rock, Guangzhou, China). His disease was diagnosed as left lung adenocarcinoma with left hilar and bilateral mediastinal lymph nodes, bilateral lungs, pleura and bone metastasis (cT4N3M1c, stage IVB).

Fig. 1
figure 1

Simulated picture of EML4-ALK and SETD2-ALK double-fusion

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The National Medical Products Administration of China (NMPA) approved alectinib for ALK-positive patients with locally advanced or metastatic NSCLC in 2018. The patient began targeted therapy with alectinib (600 mg twice daily) in October 2018. During the period of regular reexamination, the efficacy evaluation was stable disease (SD). After 26 months of treatment, the patient developed chest tightness and shortness of breath again, and chest CT showed bilateral pleural effusion and pericardial effusion again. At the same time, the lesion was enlarged than before, and a large amount of abdominal effusion appeared. No obvious tumor evidence was found in pathological examination of pleural effusion and ascites. According to the patient’s CT and condition, alectinib resistance and disease progression were considered. NGS detection was performed in pleural effusion, abdominal effusion, pericardial effusion and peripheral blood respectively, and no mutation was detected. Given the progress of the disease, pemetrexed plus carboplatin combined with toripalimab was used for six cycles from January 2021, and then maintenance treatment with toripalimab rather than pemetrexed combined toripalimab due to intolerance side effects and willingness of patient. The pulmonary lesion was slightly enlarged again after 16 months of treatment. Considering that pemetrexed had achieved good effect in the past, pemetrexed was added again. After 6 cycles of pemetrexed combined with toripalimab treatment, toripalimab maintenance treatment was performed again. At the deadline of follow-up, the patient continued to receive maintenance treatment with toripalimab. (Fig. 2)

Fig. 2
figure 2

Time axis of diagnosis and treatment

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(A) Pathological picture of adenocarcinoma. (B) CT shows disease progression after 26 months of targeted therapy with aletinib; The left interlobar fissure focus and mediastinal lymph node enlargement appeared, together with pleural effusion and new massive intraperitoneal effusion. (C) CT shows that the disease was stable after 6-cycle chemotherapy combined with immunotherapy. (D) CT shows that the left lung lesion and mediastinal lymph node were larger than before after 12 months of immune monotherapy. (E) CT shows that the lesion was stable after another 6-cycle treatment with chemotherapy and immunotherapy.

P, pemetrexed; C, carboplatin; T, Toripalimab; PD, Progressive disease; SD, stable disease.

3 Discussion

ALK mutations are most commonly caused by fusion with EML4 [11]. Approximately 61–74% of patients with EML4-ALK positive responded to ALK-TKIs. There are more than 15 different EML4-ALK fusion variants reported in NSCLC. In which V1 (E13:A20), V2 (E20:A20) and V3a/b (E6a/b:A20) are the most common. A previous retrospective study has found that variant V1/2 is more sensitive to ALK-TKIs than variant V3a/b, suggesting that different EML4-ALK variants may show different sensitivity to ALK-TKIs [12,13,14]. However, the sensitivity of fusion of “E14:A21” in this case has not been previously reported.

SETD2-ALK gene fusion is a rare ALK fusion, and it has been rarely reported in the previous studies. J. Kang et al. found that SETD2-ALK gene fusion at the DNA level expressed the EML4-ALK transcripts during mRNA maturation. It plays a role of “mediation”. In addition, the study also found that there was no significant difference in overall survival (OS) between different EML4-ALK fusion subtypes (P = 0.386), while multiple ALK fusion was significantly higher than that of EML4-ALK fusion (P = 0.01). It is possible that tumors with multiple ALK fusions are likely to be more addicted to the ALK signaling pathway, thus making the ALK-TKIs have more profound effects [14]. However, in this case, the patient with EML4-ALK and SETD2-ALK double-fusion had a progression-free survival (PFS) of 26 months after targeted therapy with alectinib, which was similar to the median PFS of 25.7 months assessed by an independent evaluator in the ALEX trial [15]. Therefore, NSCLC patients with double or compound mutations still can have response and survival benefit to targeted therapies. SETD2-ALK can be a rare fusion mutation which is sensitive to the treatment of ALK inhibitors.

Individualized treatment should be given according to the mechanism of ALK-TKIs resistance. 56% of patients with ALK gene fusion mutations developed ALK resistance mutations after the use of second-generation ALK inhibitors, with ALK G1202R becoming the most common ALK resistance mutation. The third generation ALK-TKIs, lorlatinib, can effectively inhibit the ALK resistance mutation. But in the remaining 44%, the mutation disappeared after the use of second-generation ALK inhibitors [16]. The ALUR study showed that for patients who failed to detect ALK fusion after first-line crizotinib resistance, compared with patients with ALK fusion after treatment, the objective response rate (ORR) of second-line treatment with alectinib was lower, and there was no significant improvement compared with chemotherapy. The results suggest that it may be more reasonable to choose the treatment mode of chemotherapy when ALK fusion is not detected after ALK-TKIs resistance [17]. Furthermore, a retrospective study including 20 patients with ALK fusion and disease progression after first-line aletinib treatment showed that the curative effect of ALK-TKIs in patients with secondary mutation of ALK is better than that in patients without secondary mutation of ALK (PFS: 242d vs. 75d, P = 0.05, HR = 0.46, 95% CI: 0.18–1.2). For patients without mutation, most of the them received at least first-line chemotherapy, and it was found that chemotherapy achieved better PFS (168d vs. 75d, P = 0.035, HR = 0.47, 95% CI: 0.19–1.2) than ALK-TKIs [18]. Therefore, the benefit of using ALK-TKIs is limited for patients who have ALK fusion before treatment but whose ALK fusion disappears after treatment, and the benefit may be more obvious when chemotherapy is used for subsequent treatment compared with targeted therapy.

In conclusion, this is the first report of an advanced and metastatic lung adenocarcinoma patient harbored EML4-ALK and SETD2-ALK double-fusion variation and successively response to alectinib and immunotherapy combined with chemotherapy after alectinib resistant. Loss of both EML4-ALK and SETD2-ALK double-fusion may be the mechanism of aletinib resistance for this patient. Immunotherapy combined with chemotherapy as second-line treatment may be a viable therapeutic option for NSCLC patients with double-ALK fusion when loss of double-fusion is the mechanism of ALK-TKIs resistance. However, the study also has certain limitations that must be acknowledged. During the progress of targeted treatment with aletinib, cancer cells were not found in pleural effusion, peritoneal effusion and pericardial effusion, so NSG detection of serous effusion may be negative. At the same time, the detection rate of plasma NGS detection was lower than tissues, which may affect the accuracy of NGS detection results. The consideration of ALK gene loss was more from our understanding of the disease, and there was no definite basis for it. Readers should interpret it with caution.