1084 Background: 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 (P-gp) 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. Methods: 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: 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). Conclusions: Oral paclitaxel showed very encouraging anti-cancer activity in MBC patients who failed previous chemotherapies with acceptable toxicity. Weekly oral paclitaxel can achieve paclitaxel exposure similar to that of weekly IV paclitaxel (80mg/m2) reported previously. PK of oral paclitaxel is reproducible. Clinical trial information: NCT03165955.

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