Detection of a co-mutation in the epidermal growth factor receptor gene exon 20 H773L/V774M by FoundationOne test and treatment with osimertinib: A case report

Among cases of non-small cell lung cancer (NSCLC) with EGFR mutations, NSCLC with deletions in EGFR exon 19 or 21 L858R account for 85 %. Frequency of NSCLC with minor mutations in EGFR is about 9 %, whilst EGFR exon 20 insertion mutation account for 6 % of the cases, determining it as a rare mutation. In this case, minor EGFR mutation and compound mutation EGFR H773L/V774M, were detected. Oncomine Dx target test (Oncomine), FoundationOne, and Amoy Dx polymerase chain reaction panel (Amoy 9-in-1 kit) were used as companion diagnostic tests. FoundationOne was the only one able to detect EGFR exon 20 H773L/V774M mutations. Drug therapy for NSCLC with compound mutations in EGFR exon 20 is not yet established. Unsuccessful treatments with EGFR-TKIs such as Erlotinib, Gefitinib, and Afatinib have been reported. There have also been reports of successful treatments with Osimertinib in combination with Bevacizumab. In the presented case, Osimertinib monotherapy was successful in treating NSCLC with EGFR exon 20 compound mutation. Osimertinib, therefore, has the potential to treat NSCLC with EGFR exon 20 H773L/V774M mutation, and can be a key drug for treating EGFR rare mutations.