Exon-16-skipping ERBB2 (ERBB2ΔEx16) as a novel resistance mechanism against EGFR tyrosine kinase inhibitors in non-small cell lung cancer (NSCLC).

9528 Background: In addition to ERBB2 amplification/protein overexpression, activating ERBB2 alterations have been increasingly discovered in diverse human cancers with varying incidence. ERBB2ΔEx16 is an alternatively spliced isoform of ERBB2, lacking the entire exon 16 which encodes a small extracellular domain. ERBB2ΔEx16 was recently reported to lead to oncogenic activation of ERBB2 and osimertinib resistance in EGFR T790M+ non-small cell lung cancer (NSCLC). Methods: A total of 38,680 Chinese cancer patients whose tumor specimen or circulating cell-free DNA underwent genomic profiling by targeted next-generation sequencing of cancer-related genes were retrospectively reviewed. Clinicopathological features and treatment history of ERBB2ΔEx16+ patients were evaluated. RNA sequencing was performed to validate the presence of exon-16-skipping ERBB2 at the transcriptional level. Results: A total of eighteen ERBB2ΔEx16+ patients (11 NSCLC, 2 colorectal cancer, 2 gastric cancer, and 3 others) were identified (0.047%, 18/38,680). ERBB2 exon 16 skipping may result from large fragment deletion spanning the whole or partial region of exon 16 (72.2%, 13/18), base substitution at the splice acceptor site (16.7%, 3/18) and deletion of the splice donor site (11.1%, 2/18). ERBB2 exon 16 skipping, including large fragment deletion and splice site deletion, was validated at the RNA level by RNA sequencing in 3 patients with available samples. Co-occurrence of ERBB2 amplification and ERBB2 mutations were found in 83.3% (15/18) and 50% (9/18) of cases, respectively. Concurrent copy number variations were prevalent in CDK12 (55.6%, 10/18), CDKN2B (44.4%, 8/18), NKX2.1 (38.9%, 7/18) and PTPRD (33.3%, 6/18). Among the 11 cases of ERBB2ΔEx16+ NSCLC, 9 had coexisting activating EGFR mutations (exon 19 deletions, exon 21 L858R) and received prior treatment with EGFR tyrosine kinase inhibitors (TKIs), with 2 harboring acquired EGFR T790M mutation and 1 EGFR copy number gain. Further analysis of the matched pretreatment samples in 3 EGFR-mutated NSCLC patients confirmed that ERBB2ΔEx16 was acquired during EGFR TKI therapy. In the 7 cases of other cancers, 4 to 31 non- ERBB2 mutations were identified in each sample, with TP53 being the most frequently mutated gene. Conclusions: Our data suggest that ERBB2ΔEx16 may be a general mechanism of EGFR TKI resistance in a subset of EGFR-mutated NSCLC patients, in addition to being an oncogenic driver as reported in some solid malignancies including colorectal, gastric and ovarian cancers.