OS09.6.A A MULTICENTER, PHASE I/II, OPEN-LABEL STUDY OF INTRATHECAL PEMETREXED FOR LEPTOMENINGEAL METASTASES FROM SOLID TUMOR (PMLM, NCT 05289908)

Abstract

Abstract BACKGROUND There has never been a dose-escalation study on intrathecal pemetrexed (IP) with vitamin supplementation. This phase I/II study was to evaluate the maximum-tolerated dosage (MTD) of IP with vitamin supplementation and the antitumor activity for leptomeningeal metastases (LM) from solid tumors. MATERIAL AND METHODS Phase I study followed the classic 3 + 3 design, with the dose of IP escalated from 15 mg. Phase II followed the Simon 2-stage design with the recommended dose determined in phase I. IP was administered twice per week for 2 weeks (induction therapy), followed by once per week for 4 weeks (consolidation therapy). Clinically stable or improved patients continued IP once a month (maintenance therapy). Vitamin B12 (1000 μg) and folic acid (400 μg, q.d.) were given at the beginning of treatment. Primary end points were MTD in phase I and clinical response rate (CRR) in phase I/II. All patients were assessed to investigate safety, CRR and overall survival (OS). RESULTS Between Feb 2022 and Jan 2023, 34 patients (male: 16; female: 18; age: 45-68 years; median: 56 years) were enrolled, including non-small lung cancer (20), small-cell lung cancer (3), breast cancer (8), others (3). Thirty-three patients had a confirmed LM diagnosis (positive CSF cytology). Remaining one had probable diagnosis (positive neuroimaging with typical clinical signs). Ten patients were enrolled in phase I. Three of 4 patients receiving IP at 15 mg completed induction and consolidation treatment without dose limiting toxicity (DLT). The dose was escalated to 20 mg. Two DLT (1 grade 4 hematologic toxicity and 1 grade 5 arachnoiditis) occurred in 6 patients at 20 mg. The MTD was determined to be 15 mg. Then 24 patients were enrolled in phase II and given 15 mg of IP. 82.4% (28/34) and 58.8% (20/34) patients completed induction and consolidation therapy, respectively. 41.2% (14/34) patients received maintenance therapy. Adverse events (AEs) rate was 73.5% (25/34). 50% (17/34) patients showed grade ≥ 3 AEs, including myelosuppression (11), elevation of hepatic aminotransferases (EHA) (5), elevation of blood bilirubin (EBB) (1), arachnoiditis (1), radiculitis (1), fatigue (1) and nausea (1). The overall CRR was 41.2% (14/34) by neuro-oncology proposal criteria, including 10 (29.4%) with improved neurological dysfunction, 11 (32.4%) with CSF cytological response and 4 (11.8%) with neuroimaging improvement. In a total of 28 patients receiving IP at 15 mg, 50% (14/28) patients showed grade ≥ 3 AEs, including myelosuppression (9), EHA (10), fatigue (1) and nausea (1). The CRR was 46.4% (13/28) in patients at 15 mg IP. Median survival was 7.6 (range 0.3-13.7) months in phase I, while has not yet been achieved in phase II until March 15, 2023. CONCLUSION MTD of IP was 15 mg with folic acid and vitamin B12 supplementation. IP is an optimal therapeutic option for LM from solid tumors.