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

Introduction: Brain metastases (BM) are common in patients with advanced -mutated (m+) 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 (C) and consequently limited intracranial osimertinib exposure. We investigated the relation between osimertinib C and BM development or progression.

Methods: A prospective multicenter cohort study, including patients receiving osimertinib for advanced m 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 C (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) C 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 C 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 C subgroups.

Conclusions: No relation was found between osimertinib C and BM development or progression in patients with advanced m NSCLC. This suggests that systemic osimertinib exposure is not a surrogate marker for BM development or progression.