1084 - Oral paclitaxel in the treatment of metastatic breast cancer (MBC) patients Dai MS 1 , Chao TY 2 , Chao TC 3 , Chiu CF 4 , Lu YS 5 , Shiah HS 6 , YY Wu 1 , WH Cheng 2 , Hung N 7 , Fetterly G 7 , Cutler DL 7 , Kwan R 7 , Kramer D 7 , Chan W 7 , Hung T 8 1 Division of Hematology/Oncology, Tri-Service General Hospital, Taipei, Taiwan., 2 Division of Hematology-Oncology, Taipei Medical University- Shuang Ho Hospital, New Taipei City,Taiwan . 3 Division of Medical Oncology, Taipei Veterans General Hospital, BeitouDistrict, Taipei, Taiwan, 4 Department of Medical Oncology, China Medical University Hospital, Taichung, Taiwan, 5 Department of Medical Oncology, National Taiwan University Hospital, Taipei, Taiwan, 4Department of Medical Oncology, China Medical University Hospital, Taichung, Taiwan, 5Department of Medical Oncology, National Taiwan University Hospital, Taipei, Taiwan 7 University of Otago, Dunedin, New Zealand 7 Athenex, Buffalo, NY, 8 Zenith Technology Corporation Limited, Dunedin, New Zealand. ClinicalTrials.gov Identifier: NCT03165955 INTRODUCTION Intravenous (IV) paclitaxel is an effective treatment for breast cancer. Oral administration paclitaxel is preferable to IV regarding minimizing IV injections, anaphylactic reactions to cremaphor, steroid pre- medications, hospital visits, and relevant costs. However, paclitaxel has poor oral absorption due to active excretion by P-glycoprotein (Pgp) in the intestinal cells. Oraxol (Athenex, USA) is an oral paclitaxel and HM30181, a novel oral inhibitor of intestinal P-gp which enables the oral administration of paclitaxel. We report the final results of a pharmacokinetics (PK) study, including clinical response and tolerability of Oraxol in treatment of metastatic breast cancer patients. Multicenter, single-arm, open-label, PK study of Oraxol (HM30181A at 15mg, plus oral paclitaxel 205mg/m2) administered orally for 3 consecutive days weekly for up to 16 weeks. Paclitaxel PK was assessed at week-1 and week- 4. Tumor Response was measured at weeks 8 and 16 using RECIST criteria 1.1. Toxicity was assessed using CTCAE v4.03. RESULTS MATERIALS AND METHODS Twenty-eight MBC patient were studied with a mean age of 56.6 years (range: 38 - 79 yrs). 26 patients had failed mutiple previous chemotherapies. There were 11 (42.3%) partial response, 12 (46.2%) stable disease and 3 (11.5%) progressive disease in 26 evaluable patients. Three patients had treatment-related SAEs (grade ≥3 neutropenia) and all patients recovered completely. PK results showed that the AUC of oral paclitaxel at week-1 was reproducible at week-4 (3050 to 3594 ng-hr/mL). CONCLUSION 1. Weekly oral paclitaxel can achieve paclitaxel exposure similar to that of weekly IV paclitaxel (80mg/m2) reported previously. PK of oral paclitaxel is reproducible. 2. Oraxol appears effective in the treatment of advanced breast cancer patients. The tumor response rate (PR= 42.3%, SD= 46.2%) of Oraxol in treatment of metastatic breast cancer patients who failed previous chemotherapies is very encouraging. 3. The drug toxicity profile of Oraxol appears tolerable HM30181: MOA