Late recurrence of lung adenocarcinoma harboring EGFR exon 20 insertion (A763_Y764insFQEA) mutation successfully treated with osimertinib.

The EGFR-A763_Y764insFQEA is a unique mutation among EGFR exon 20 insertion mutations in that it is associated with sensitivity to conventional EGFR-tyrosine kinase inhibitors. This mutation, which was not initially covered by conventional reverse transcription polymerase chain reaction (RT-PCR) genotyping method, has only been detected in clinical practice when a next-generation sequencing (NGS)-based cancer panel is implemented. We present the case of a female patient with recurrent lung adenocarcinoma from a lung tumor resected 10 years earlier. Sequential single-gene investigations and the OncomineTM Comprehensive Assay (ver.3) analysis of the recurrent tumor did not reveal any targetable driver mutations. However, the second NGS analysis with the OncoGuideTM NCC oncopanel found the EGFR-A763_Y764insFQEA mutation after tumor progression with carcinomatous lymphangiomatosis and multiple brain metastases. Osimertinib treatment improved her condition immediately. The identical EGFR-A763_Y764insFQEA mutation was detected in the tumor resected 10 years earlier. Based on this common mutation the patient was diagnosed with late recurrence of lung cancer harboring the EGFR-A763_Y764insFQEA mutation. The OncoGuideTM NCC oncopanel covered whole exons of the EGFR gene and was able to detect this mutation. In the present clinical practice, the EGFR-A763_Y764insFQEA mutation is the only treatable mutation among EGFR Ex.20 insertion mutations. We need to understand the gene mutation profile identified by each panel and consider reexamining them for this mutation.