MO45-3 the Efficacy of Osimertinib in Patients with EGFR-positive Non-Small Cell Lung Cancer with Malignant Pleural Effusion

Malignant pleural effusion (MPE) is considered to be one of the poor predictive factors in epidermal growth factor receptor (EGFR) mutation-positive non-small-cell lung cancer (NSCLC). However, the efficacy of osimertinib for patients with MPE has not been clarified. We retrospectively evaluated the efficacy of osimertinib in view of PFS and sites of relapse in patients with EGFR T790M secondary mutation after prior EGFR-TKIs and in patients with EGFR-TKIs naÏve at the Cancer Institute Hospital of JFCR. The median PFS was evaluated from the initiation of osimertinib. We defined base-line MPE (BL-MPE) as pleural effusion with a thickness of 10 mm or more shown by chest computed tomography at the initiation of osimertinib. In addition, MPE increase at the time of disease progression was defined as MPE-PD. A total of 232 patients who had osimertinib were enrolled from April 2016 to July 2021, 119 patients were with T790M mutation and 113 patients were EGFR-TKIs naÏve. 39 and 46 patients of each group had BL-MPE, respectively. In patients with T790M mutation, the median PFS in those with or without BL-MPE was 12.1 months and 11.8 months (HR 0.95 [95%CI: 0.63-1.45], p=0.82). 30 of 39 (76.9%) patients with BL-MPE and 75 of 80 (93.8%) without BL-MPE were confirmed relapses to osimertinib. MPE-PD was significantly more frequent in patients with BL-MPE than those without BL-MPE (8 of 30 vs 2 of 75, respectively; chi-Sq test: p=0.0002). In patients with EGFR-TKIs naÏve, the median PFS was also similar in patients with or without BL-MPE (26.4 months vs 19.4 months, respectively; HR 0.93, p=0.98). The relapse was confirmed in 17 of 46 (40.0%) with BL-MPE and 27 of 67 (40.3%) without BL-MPE, 4 and none of them manifested MPE-PD, respectively. The number of cases was immature. We did not show the efficacy of osimertinib is poor in patients who have EGFR mutation-positive NSCLC with MPE. MPE-PD was seen frequently in patients with BL-MPE.