Complete response to first-line osimertinib monotherapy in a complex epidermal growth factor receptor mutant (L833V/H835L) lung adenocarcinoma patient: a case report

Although uncommon epidermal growth factor receptor (EGFR) mutations account for 10-15% EGFR mutant non-small cell lung cancer (NSCLC) patients, clinical evidence for uncommon EGFR mutations, such as complex mutations remain limited. In this study, we reported a NSCLC patient harboring complex EGFR L833V / H835L mutation in exon 21, who had a complete response to first-line osimertinib monotherapy. The patient admitted to our hospital for space-occupying lesions of right lower lung during an annual health checkup, and was diagnosed as stage IIIA lung adenocarcinoma. Targeted next-generation sequencing (NGS) on tumor samples showed a complex EGFR mutation: L833V / H835L in exon 21. Therefore, she was treated with osimertinib monotherapy and complete remission achieved soon. During follow-up period, no metastasis was found and serum carcinoembryonic antigen returned to normal. In addition, NGS monitoring of mutations in circulating tumor DNA maintained negative. The patient remain benefitted for osimertinib monotherapy over 22 months with no disease progression. Our case firstly provided clinical evidences of first-line osimertinib therapy in lung cancer patients with rare L833V / H835L EGFR mutation.