Osimertinib-induced DNA resistance mutations in cerebrospinal fluid of EGFR mutated NSCLC patients developing leptomeningeal metastases: ORA-LM study.

BACKGROUND: Diagnosis and treatment of leptomeningeal metastases (LM) in epidermal growth factor receptor mutation positive (EGFRm+) NSCLC is challenging. We aimed to identify resistance mechanisms (RM) to osimertinib in cerebrospinal fluid (CSF) and plasma. METHODS: EGFRm+ patients with new or progressive LM during osimertinib were enrolled. NGS Ampliseq was performed on DNA isolated from CSF. Patients were prescribed osimertinib dose escalation (DE, 160mg QD) following lumbar puncture. Clinical and radiological response was evaluated four weeks after osimertinib DE. RESULTS: Twenty-eight patients were included. The driver mutation was identified in 93% of CSF samples (n=26). Seven (27%) harbored ≥1 RM. Twenty-five patients (89%) were prescribed osimertinib DE. Four weeks afterwards, symptoms improved in five patients, stabilized in nine and worsened in eleven patients. Twenty-one (84%) patients underwent MR imaging. Four showed radiological improvement, fourteen stabilization, and three worsening. CONCLUSIONS: In 27% of patients an RM was found in CSF ctDNA, none of which are targetable at time of writing, and clinical efficacy of osimertinib DE seems limited. There is much to gain in diagnostic as well as therapeutic strategies in EGFRm+ NSCLC LM.

Osimertinib Plasma Trough Concentration in Relation to Brain Metastases Development in Patients With Advanced EGFR-Mutated NSCLC.

Introduction: Brain metastases (BM) are common in patients with advanced EGFR-mutated (EGFRm+) NSCLC. Despite good BM-related outcomes of osimertinib, several patients still experience intracranial progression. A possible explanation is pharmacologic failure due to low plasma trough levels (Cmin,SS) and consequently limited intracranial osimertinib exposure. We investigated the relation between osimertinib Cmin,SS and BM development or progression. Methods: A prospective multicenter cohort study, including patients receiving osimertinib for advanced EGFRm+ NSCLC. At osimertinib start, patients were allocated to the BM or no or unknown BM cohort and were further divided into subgroups based on osimertinib Cmin,SS (low, middle, and high exposure). Cumulative incidence of BM progression or development and overall survival were determined for each group. Results: A total of 173 patients were included, with 49 (28.3%) had baseline BM. Of these patients, 36.7% experienced BM progression, of which 16.7% in the low (<159.3 ng/mL), 40.0% in the middle, and 47.1% in the high (>270.7 ng/mL) Cmin,SS subgroups. After 12 months, the cumulative incidence of BM progression for the BM cohort was 20% (95% confidence interval [CI] 2.6-49.0), 31% (95% CI:10.6-53.9), and 31% (95% CI:10.8-54.5) per Cmin,SS subgroup, respectively. After 20 months, this was 20% (95% CI:2.6-49.0), 52% (95% CI:23.8-74.2), and 57% (95% CI:24.9-79.7), respectively. For the no or unknown BM cohort, 4.0% developed BM without differences within Cmin,SS subgroups. Conclusions: No relation was found between osimertinib Cmin,SS and BM development or progression in patients with advanced EGFRm+ NSCLC. This suggests that systemic osimertinib exposure is not a surrogate marker for BM development or progression.