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Poster session 03

408P - Proxalutamide plus endocrine therapy as a combination therapy in women with HR+/HER2-/AR+ metastatic breast cancer: A phase I study

Date

21 Oct 2023

Session

Poster session 03

Topics

Endocrine Therapy;  Targeted Therapy

Tumour Site

Breast Cancer

Presenters

Huiping Li

Citation

Annals of Oncology (2023) 34 (suppl_2): S334-S390. 10.1016/S0923-7534(23)01260-7

Authors

H. Li1, H. Jiang1, G. Song1, R. Ran1, J. Wang1, X. Wang2, J. Huang2, J. Feng3, L. zhang3, A. Zang4, H. Yang4, Y. Pan5, X. he6, M. Donng6, Y. Tong7, Z. Wang8, Z. Shao8

Author affiliations

  • 1 Department Of Breast Oncology, Peking University Cancer Hospital and Institute, 100142 - Beijing/CN
  • 2 Department Of Medical Oncology, Zhejiang Cancer Hospital - Cancer Research Institute, 310022 - Hangzhou/CN
  • 3 Department Of Medical Oncology, Jiangsu Cancer Hospital, 210009 - Nanjing/CN
  • 4 Department Of Medical Oncology, Affiliated Hospital of Hebei University, Hebei/CN
  • 5 Department Of Medical Oncology, Anhui Provincial Hospital, 230001 - Hefei/CN
  • 6 Department Of Clinical Research, Suzhou Kintor Pharmaceuticals Inc., 215123 - Suzhou/CN
  • 7 Ceo, Suzhou Kintor Pharmaceuticals Inc., 215123 - Suzhou/CN
  • 8 Department Of Breast Oncology, Fudan University Shanghai Cancer Center, 200032 - Shanghai/CN

Resources

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Abstract 408P

Background

This phase I clinical study aimed to assess the safety, efficacy and pharmacokinetic (PK) characteristics of proxalutamide, in combination with Endocrine therapies (ETs), in hormone-receptor (HR)+/human epidermal growth factor receptor 2 (HER2-)/AR+ metastatic breast cancer (mBC).

Methods

In part 1 of the study, patients who progressed on multiple lines of therapy (≥1) were enrolled. Monotherapies were initiated including letrozole (2.5 mg/day on days 1-14) for cohort A, exemestane (25 mg/day on days 1-14) for cohort B, and fulvestrant (intramuscularly 500 mg once on days 1, 15 and 28) for cohort C, followed by proxalutamide 200 mg QD and ETs for in a 28-day cycle. In part 2 of the study, patients who either progressed on or were not tolerant to the first-line therapy were enrolled to receive proxalutamide 200 mg QD plus fulvestrant [cohort D] at a dose of 500 mg once on days 1 and 15 and day 1 of each cycle thereafter. The primary endpoint is safety and tolerability. PK and antitumor activity were also assessed.

Results

Between June 18, 2019 and Sep 5, 2022, 37 (17 in part 1 and 20 in part 2) patients received the combination therapy. No DLTs or drug-related SAEs were reported. The commonly reported Grade ≥3 TEAEs were neutrophil count decreased (3/37, 8.1%), hypokalemia (3/37, 8.1%) and bone marrow suppression (3/37, 8.1%). 6 (15.8%) patients on proxalutamide plus fulvestrant achieved a partial response and 13 (34.2%) patients had stable disease, with an overall disease control rate of 50.0% (95% CI, 33.4%–66.6%; 38.9% in part 1 and 60.0% in part 2). The overall median PFS was 6.4 months (95% CI, 2.7-19.3) for cohort C and 11.0 months (95%CI: 5.5-NA) for cohort D. PK profiles indicated rapid absorption of proxalutamide following a single dose. After multiple doses, proxalutamide and its major metabolite reached steady-state serum concentration levels at day 29 and exhibited a tendency for drug accumulation.

Conclusions

This study suggested a good antitumor activity and safety profile of the combination therapy of proxalutamide and fulvestrant for HR+/HER2-/AR+ mBC patients in the ≥2nd-line settings. Moreover, it may provide survival benefits for these patients, warranting further investigation in a larger population.

Clinical trial identification

CTR20191063.

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Suzhou Kintor Pharmaceuticals.

Disclosure

All authors have declared no conflicts of interest.

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