EGFR exon 20 insertion mutations and response to osimertinib in non-small-cell lung cancer

The study included a cohort of patients who were referred to OrigiMed (Shanghai, China) for targeted next generation sequencing (NGS) test in China between August 2016 and July 2018. Patient samples and clinical information including gender, age and histologic subtypes were retrieved at the time of referral. Six patients with EGFRex20ins mutant stage IV NSCLC who were treated with osimertinib 80 mg once daily were included to evaluate the antitumor activity of osimertinib. Data were retrospectively collected from digital medical records. The study was approved by the Institutional Review Board of SYSUCC and written informed consent was obtained for each patient prior to sample collection. Written consents were obtained from parents if patients were under 16 years old.

DNA from Formalin-fixed, paraffin-embedded tumor tissue and matched blood samples was extracted. Comprehensive genomic profiling was performed by NGS with a 37 or 450 cancer related gene panel covering the whole exons of EGFR gene at a mean coverage depth of >800X (1547 cases with 37 panel, and 769 cases with 450 panel). The genomic alterations including single base substitution, insertions/deletions, copy number variations, as well as gene rearrangement and fusions were assessed. As for six patients treated with osimertinib, genetic status was also determined through NGS prior to osimertinib.

All six patients received oral osimertinib 80 mg once daily. Radiological follow-up was performed at the first months then once every 2 months with computed tomography (CT) of the thorax and upper abdomen. Regular cerebral magnetic resonance imaging (MRI) with CT was carried out once any patient was confirmed brain metastasis. Response was assessed according to Response Criteria in Solid Tumors (RECIST) 1.1 [30]. Progression-free survival (PFS) was defined as the interval from the date of initiation of osimertinib therapy to the date of disease progression or death from any cause, whichever occurred first.

Among the 2316 unselective NSCLC tumors, EGFR mutations were identified in 1095 cases (47.3%). EGFRex20ins mutations were detected in 53 cases, contributing 2.3% of all NSCLC cases and 4.8% of EGFR-mutant tumors. Compared with Foundation Medicine (FM) data representing the largest EGFRex20ins cohort, we found that although EGFR mutations were much more common in our Chinese NSCLC patients than that of Western population (47.3% vs 15.5% in FM), EGFRex20ins mutation represented a much smaller group in EGFR mutant NSCLC (4.8% vs 11.7% in FM, p < 0.001) [17]. Of note, our result was comparable with FM cohort in frequency of EGFRex20ins in total NSCLC (2.3% vs. 1.8% in FM, p = 0.12, Fig. 1). The smaller proportion of EGFRex20ins in Chinese populations is due to the larger scale of EGFR mutations than western groups.

The demographic and clinical characteristics of these patients are summarized in Tables 1 and 2. Of the patients with EGFR mutations, EGFRex20ins ranked the fourth most common type, following EGFR exon 19 deletions (436/1095, 39.8%), L858R (410/1095, 37.4%) and T790 M mutations (58/1095, 5.3%) (Fig. 2a). The majority of EGFRex20ins mutations were identified in lung adenocarcinoma (92.5%, 49/53). EGFRex20ins were also detected in two adenosquamous cases and two NSCLC not otherwise specified (NOS). Median age of patients with exon 20 insertion is 57 (31–85) years.

In total, 20 different variants of exon EGFRex20ins were identified in 53 NSCLC patients. The most frequent variant is A767_V769dup (32.1%, 17/53), followed by P772_H773dup (4/53, 7.5%), S768_D770dup (4/53, 7.5%), N771_H773dup (4/53, 7.5%), A763_Y764insFQEA (3/53, 5.7%). Unique EGFRex20ins mutations detected by NGS were summarized in Fig. 2b.

EGFRex20ins tended to be exclusive with NSCLC driver genes such as EGFR mutation ERBB2, ALK, BRAF and RET mutations. The most common co-mutations were TP53 (49.1%). Co-mutation pattern compared with EGFR ex19dels, L858R, T790 M and other EGFR uncommon mutations were summarized in Additional file 1: Figure S1 and Additional file 2: Figure S2.

From August 28th, 2017 to April 30th, 2018, six patients with stage IV lung adenocarcinoma bearing EGFRex20ins started osimertinib treatment. Median follow-up time was 6.2 months. Previous treatment, detailed mutation characteristics and the outcome of osimertinib are shown in Table 3. All the patients had stage IV lung adenocarcinoma and predominantly females (5/6). Before osimertinib treatment, four patients were observed metastasis in lungs and pleura. Patient 5 was diagnosed with brain metastasis and patient 6 with bone metastasis. The median age is 64 years old. Two patients received osimertinib as first line therapy and two patients had previous treatment with other EGFR TKIs. Per RECISIT 1.1, four (67.7%) patients achieved partial response (PR) and the remaining two patients (33.3%) obtained stable disease (SD). Median progression-free survival (PFS) was 6.2 months (95% confidence interval 5.0–12.9 months; range 4.9–14.6 months). Treatment-related adverse events (AEs) included diarrhea (2/6), pruritus (2/6), stomatitis (1/6) and nausea (1/6). No grade 3 or more AEs were documented. At data cut-off (December 1st, 2018), Two patients had sustaining disease control and remained on osimertinib treatment, while the other four patients had progressive disease (PD) ultimately.

Patient 1 had EGFR A767_V769dup mutation and received first-line therapy with osimertinib. The patient achieved PR and the PFS was 6.0 months. PR was also observed in patient 2 (EGFR S768_D770dup), with a PFS of 14.6+ months. The patient was still on treatment at data cutoff. Patient 3 was identified with a novel EGFRex20ins mutation (EGFR N771_P772insL), which had not been reported before. The patient had SD as best response under first line osimertinib treatment and transferred to other treatment after 4.9 months due to enlarged pleural nodules. Patient 4 harbored the same EGFRex20ins mutation as that of patient 2 and attained SD with a PFS of 11.2+ months. Both patient 2 and patient 4 remained on osimertinib treatment. Patient 5 was confirmed with multiple cerebral metastasis and experienced dizzy and vomiting when diagnosed as stage IV adenocarcinoma. The patient was treated with first line chemotherapy with the best response of PD. Thereafter, the patient started osimertinib and exhibited salient clinical improvement and a reduction of nearly half the tumor burden. The patient had PD finally due to new onset bone metastasis, with a PFS of 6.4 months. Patient 6 was initially diagnosed as lung adenocarcinoma harboring EGFR A763_Y764insFQEA. The patients started gefitinib treatment with a best response of PR and PFS of 9.0 months. At disease progression, the patients had rebiopsy and his tumor was found to had EGFR A763_Y764insFQEA and EGFR T790 M. Thereafter, the patient was treated with osimertinib and attained PR. The patient experienced PD eventually due to brain metastasis and achieved a PFS of 5.1 months. CT scans performed prior to (baseline) and after osimertinib treatment are demonstrated in Fig. 3. Tumor shrinkage for each patient is shown in Fig. 4.