A 58-year-old woman with advanced adenocarcinoma of the lung (stage IV, brain metastases) is found to have an EGFR exon 19 deletion mutation on molecular testing. She has never smoked. What is the drug of choice for first-line treatment?

Explanation

## First-Line Treatment of EGFR-Mutant Advanced NSCLC **Key Point:** Osimertinib is the preferred first-line tyrosine kinase inhibitor (TKI) for EGFR-mutant (exon 19 deletion or L858R) advanced NSCLC, including patients with CNS metastases. ### Why Osimertinib? **High-Yield:** Osimertinib is a third-generation, irreversible EGFR TKI with superior CNS penetration and activity against both sensitizing mutations (exon 19 deletion, L858R) and acquired T790M resistance mutations. The FLAURA trial demonstrated that osimertinib as first-line monotherapy provides superior PFS and OS compared to first-generation TKIs (gefitinib, erlotinib). **Clinical Pearl:** Osimertinib achieves high concentrations in the CSF and brain tissue, making it ideal for patients with brain metastases. It is the only TKI recommended as monotherapy (without chemotherapy) for treatment-naïve EGFR-mutant NSCLC. ### Mechanism & Efficacy | Feature | Osimertinib | Gefitinib | First-Gen TKI Combo | |---------|------------|----------|---------------------| | Generation | 3rd (irreversible) | 1st (reversible) | 1st + chemotherapy | | CNS penetration | High | Moderate | Variable | | EGFR ex19del activity | ✓✓✓ | ✓✓ | ✓✓ | | T790M resistance | Covers | Does not cover | Does not cover | | First-line OS benefit | Yes (FLAURA) | No vs osimertinib | Inferior to osimertinib monotherapy | | Typical dose | 80 mg daily | 250 mg daily | Varies | **Mnemonic:** **OSI**mertinib = **O**ptimal **S**ingle-agent **I**nhibitor for EGFR-mutant NSCLC. ### Why Not the Other Options? 1. **Gefitinib (first-generation TKI):** FLAURA trial showed osimertinib superior PFS (18.9 vs 10.2 months) and OS. Gefitinib is now reserved for patients intolerant to osimertinib or in resource-limited settings. 2. **Chemotherapy-based regimens (cisplatin + pemetrexed ± bevacizumab):** Inferior to TKI monotherapy in EGFR-mutant disease. Chemotherapy is used only if TKI resistance develops or TKI is contraindicated. 3. **Carboplatin + paclitaxel:** Standard for EGFR wild-type NSCLC, not EGFR-mutant disease. **Warning:** Do not confuse first-line osimertinib (for treatment-naïve EGFR mutation) with second-line osimertinib (for acquired T790M resistance after first-generation TKI failure). Both are indicated, but the context differs.