(Breast Cancer) Phase III Trial Report on Oral Paclitaxel Plus Encequidar in Metastatic Breast Cancer

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This article is a summary of international medical information and is not medical advice; it cannot replace the diagnosis or treatment plan of your attending physician. The medical technologies, drug information and clinical data presented here are compiled from public literature and official statements of Japanese medical institutions; the applicability and outcome of any therapy vary with each patient and must be assessed individually by a qualified physician.

Any specific treatment plan must be assessed by a licensed physician in Japan

Regulatory status in Japan (checked November 4, 2026): Encequidar (oral paclitaxel plus encequidar) is not approved in Japan; no Japanese marketing approval or Japanese package insert was found. This article only summarizes overseas research reports. It is not an assessment of the treatment and is not medical or treatment advice.

On July 20, 2022, Hope S. Rugo and colleagues at the University of California San Francisco published online in the Journal of Clinical Oncology the results of an open-label, randomized Phase III trial (NCT02594371). The trial compared oral paclitaxel combined with the P-glycoprotein inhibitor encequidar with intravenous (IV) paclitaxel in metastatic breast cancer.

Trial design

402 women with metastatic breast cancer enrolled in Latin America, randomized 2:1
Oral paclitaxel 205 mg/m² plus encequidar 15 mg on 3 consecutive days each week (265 patients) vs IV paclitaxel 175 mg/m² every 3 weeks (137 patients)
Primary endpoint: confirmed radiographic response assessed by blinded independent central review; secondary endpoints: progression-free survival and overall survival

Reported results

Confirmed response rate: 36% (oral) vs 23% (IV)
Median progression-free survival: 8.4 vs 7.4 months; median overall survival: 22.7 vs 16.5 months (the overall survival difference was not statistically significant, P = 0.08)
Grade 3–4 adverse reactions: 55% vs 53%
Neuropathy above grade 2: 2% vs 15%; alopecia: 49% vs 62%
The oral group had more nausea, vomiting, diarrhea and neutropenic complications, particularly in patients with elevated liver enzymes at baseline; treatment-related on-study deaths: 3% (oral) vs 0% (IV)

Regulatory status

In 2021 the US FDA issued a Complete Response Letter for this oral regimen and did not approve it. Encequidar is also not approved in Japan.

Points to consider

These are results from a single trial and cannot be applied directly to individual patients; safety findings such as serious infections in the oral group also need to be taken into account.

Source: Rugo HS, et al. J Clin Oncol. 2023;41(1):65-74 (published online July 20, 2022). https://ascopubs.org/doi/full/10.1200/JCO.21.02953

Note: This article summarizes overseas clinical research for reference only and is not medical or treatment advice. Study data do not predict outcomes for individual patients. Please refer to the original source and discuss any treatment decisions with your physician.

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