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Clinical characteristics of EGFR fusion patients
In total, 0.303% (106/35023) of patients in our cohort harbored EGFR fusion. EGFR fusion is classified into variant type 1 and type 2 according to the direction of fusion and the principle of activation. Variant type 1 is EGFR-X, which may result in the loss of the EGFR autophosphorylation site in the C-terminal tail of the receptor [20]. Variant type 2 is the “X-EGFR” and has a common fusion activation mechanism in which the partner gene leads to the activation and continued expression of the EGFR protein. All 106 EGFR fusions included the full EGFR kinase domain, which is encoded by exons 18–24. As seen in Fig. 1A, we present a schematic with an EGFR parterner gene occurred ratio higher than 4%. The activation and treatment effectiveness with TKI have been reported in both EGFR fusion variant types [22, 23]. Patient characteristics are summarized in Table 1. Patients’ age ranged from 5 to 82 years, with a median age of 60.5 years. Sixty-three (59.43%) patients were male, and 43 (40.57%) were female. A total of 51.89% had clinical-stage III/IV disease versus 5.66% with stage I-II disease, and other stages were unavailable (NA). Among the top two cancers, adenocarcinoma (31, 64.58%) predominates in lung cancer, and glioblastoma (16, 48.48%) predominates in glioma. Variant type 1 accounted for 53.77%, variant type 2 accounted for 37.74%, and contained both two variant types accounted for 8.49%.
Table 1
Baseline characteristics of patients with EGFR fusion (n = 106)
Characteristics | N (%) |
Age, years Median (range) | 60.5(5–82) |
Male gender | 63(59.43%) |
Cancer type Liver cancer Colorectal cancer Biliary tumors Pancreatic cancer Lung cancer Bone and Soft Tissue Sarcoma Gastric cancer Breast cancer Cervical cancer Glioma Medatloblastoma Gastroesophageal junction cancer others | 1(0.94%) 3(2.83%) 1(0.94%) 1(0.94%) 48(45.28%) 2(1.89%) 11(10.38%) 2(1.89%) 1(0.94%) 33(31.13%) 1(0.94%) 1(0.94%) 1(0.94%) |
Stage I II III IV NA | 3(2.83%) 3(2.83%) 18(16.98%) 37(34.91%) 45(42.45%) |
Pathology Lung cancer Adenocarcinoma, ADC squamous cell carcinoma, SQCC NA Glioma Astrocytoma Glioblastoma NA | 48 31(64.58%) 2(4.17%) 15(31.25%) 33 5(15.15%) 16(48.48%) 12(36.36%) |
Fusion variant type Variant type 1 Variant type 2 Variant types 1 and 2 | 57(53.77%) 40(37.74%) 9(8.49%) |
Table 2
The frequency of EGFR fusion in different cancer types in TCGA
Cancer type | Patients (N) | EGFR fusion (N) | Percentage (%) |
Glioma | 1094 | 16 | 1.46 |
Bladder Urothelial Carcinoma | 410 | 3 | 0.73 |
Head and Neck squamous cell carcinoma | 522 | 3 | 0.57 |
Stomach adenocarcinoma | 435 | 2 | 0.46 |
Lung cancer | 986 | 2 | 0.20 |
Liver hepatocellular carcinoma | 371 | 1 | 0.27 |
Others | 5745 | 0 | 0 |
In total, EGFR fusions were detected in 0.303% (106/35,023) of the patients, with varying frequencies across diverse tumor types. Lung cancer exhibited a prevalence of 0.236% (48/20,345), glioma 1.370% (33/2,409), gastric cancer 0.676% (11/1,627), colorectal cancer 0.084% (3/3,582), breast cancer 0.743% (2/269), bone and soft tissue sarcoma 0.277% (2/721), and a single case of EGFR fusion was identified in gastroesophageal junction cancer, medulloblastoma, cervical cancer, pancreatic cancer, biliary tumors, liver cancer, and other types as shown in Fig. 1B.
2. Identification of EGFR fusion partners in patients with different cancer types
The partner genes of the two fusion types are shown in Fig. 2A-B. SEPT14, ELDR, and LOC100996654 are the most frequent in variant type 1. ELDR and LOC100996654 are the most common in variant type 2. The fusion partner genes are also different in various cancer types. The partner genes in different cancer types are shown in Supplementary Fig. 1A-B. The chromosome distribution of the fusion partner gene of the two types is shown in Fig. 2C-D and the partner genes are scattered across the chromosomes. Breakpoint positions of different EGFR fusion variant types are shown in Fig. 2E. The breakpoints of EGFR in lung cancer patients were concentrated in exons 15, 16, 27, and 28. In glioma patients, breakpoints of EGFR were concentrated in exons 7, 8, 24, and 25. The breakpoints of EGFR in other cancer types are scattered.
3. Co-occurrence genetic mutants and TMB of patients harboring EGFR fusion
Among 106 patients with EGFR fusion, 55 patients' tumors were examined by NGS using a 539-gene panel, and the co-mutation status of these patients is shown in Fig. 3A. Among the 55 patients with EGFR fusion, 31 (56%) patients combined with EGFR amplification, and 26 (47%) patients combined with EGFR single nucleotide variants (SNV, including missense mutation, in-frame deletion, in-frame insertion and multi-hit) mutations. Notably, there were 19 (35%) patients with sensitive mutations. The top 5 genes that co-mutated with EGFR fusion were TP53 (mutation frequency, MF: 65%), BRCA2 (MF: 43%), ALK (MF: 41%), MUC16 (MF: 39%), and MYC (MF: 39%).
The median TMB among the 55 patients with EGFR fusion was 17.75 (0.71-139.01) Muts/Mb in solid tumors. The median TMB was 14.88 (0.71-139.01) in the 26 lung cancer patients, 18.45 (1.42–63.83) in the nine gastric cancer patients and 2.33 (0.71–4.26) in the eight glioma patients. There were 14 patients with TMB-high (≥ 10 Muts/Mb) and 41 with TMB-low (< 10 Muts/Mb). There was no significant difference in TMB between EGFR fusion and non-EGFR fusion groups, whether among pan-cancer (p = 0.054), lung cancer (p = 0.28), glioma (p = 0.27) or gastric cancer patients (p = 0.11, Supplementary Fig. 2).
Among 106 patients with EGFR fusion, there were 77 patients combined with EGFR CNV and 62 patients combined with EGFR SNV (including L858R, 19 exon deletion, L861Q, T790M, 20 exon insertion and so on; Fig. 3B). The types of EGFR mutations that only occurred in lung cancer were L858R, L861Q, T790M and 20exon insertion. The EGFR mutations are different in lung cance rand glioma. In lung cancer, EGFR mutations mostly occurred in functional kinase domain, mainly TyrKc. But in glioma, the most common EGFR mutation is EGFRvIII mutation may be caused by deletion of exons 2–7 (Fig. 3C, D). These results are basically consistent with the results reported in other previous studies [14–16, 19].
4. The prognostic impact of EGFR fusions
We collected 9,563 tumor variant data in 30 cancer types from TCGA to calculate the proportion of EGFR fusions, and 27 (0.28%) samples were identified harboring EGFR fusions in six cancer types, including 22 patients with variant type I and 5 patients with variant type II. The proportion of glioma was the highest (16/1094, 1.46%), followed by bladder urothelial carcinoma (3/410, 0.73%) and head and neck squamous cell carcinoma (3/522, 0.57%) (Table 2). Notably, there was no co-mutant EGFR-sensitive mutation, but 26 EGFR CNV co-mutations were found among the 27 patients with EGFR fusion.
We further explored the relationship between EGFR fusion and overall survival (OS) in the TCGA cohort. Patients with EGFR-fusion had a significantly shorter OS than those without EGFR fusion in pan-cancer (p < 0.0001, Fig. 4A) and in glioma (p = 0.028, Fig. 4B), suggesting that EGFR fusion might be a high-risk factor for poor prognosis. Notably, there were 26 EGFR amplification co-mutations among the 27 EGFR fusion samples. Therefore, we specifically detected the relationship between EGFR fusion, only the EGFR amplification group and others (without EGFR fusion and EGFR amplification). The results showed that in pan-cancer, the EGFR fusion group had the worst OS, and the EGFR CNV group had a comparably worse OS than others group (p < 0.0001, Fig. 4C). In glioma, the EGFR fusion and the EGFR amplification groups had a comparably worse OS than others group (p < 0.0001, Fig. 4D).
5. Case presentation
A 71-year-old male patient was admitted to the hospital for 15 days with an irritant cough and two days with bloody sputum. A space-occupying lesion in the left upper lobe was discovered using computed tomography (CT) (Fig. 5A). Following the appropriate preoperative examination, a left total pneumonectomy was performed on November 2, 2020 (Fig. 5B). Percutaneous lung biopsy yielded a diagnosis of lung adenocarcinoma. Finally, the disease was diagnosed as stage IIIA (T1bN2M0). The patient then received postoperative adjuvant chemotherapy for six months, CT results were shown in Fig. 5C. To seek targeted therapy, formalin-fixed and paraffin-embedded specimen (FFPE) samples were analyzed by NGS, and a novel EGFR-SEPT14 (11.36% abundance) fusion was detected (Fig. 5E-F). Several other mutations, such as TP53, CCNE1 and HRAS were also observed (Supplementary Table 1). The patient was then given almonertinib mesilate tablets (500 mg daily) and remained relapse-free until July 8, 2023 (Fig. 5D).