Osimertinib and chemotherapy combination to treat brain metastasis flare and osimertinib resistance by EGFR C797S.

Chemotherapy or involvement in a clinical trial remain the standard treatment for patients with EGFR mutant non-small cell lung cancer who have disease progression while receiving Osimertinib. Rapid progression, also known as flare-phenomenon, has been described after discontinuation of tyrosine kinase inhibitors. In this case, we describe a young woman who has extracranial progressive disease due to EGFR C797S resistance mutation while being treated with osimertinib, with a rapid neurological deterioration after osimertinib withdrawal due to flare-phenomenon progression in the brain, and a prompt intracranial response with osimertinib reintroduction in addition to chemotherapy to achieve extracranial diseases control.