Phase 3 Trial of Fablyn Plus Verzenio for Metastatic Breast Cancer Initiates Registration

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Pre- and post-menopausal patients with locally advanced or metastatic ER+/HER2- breast cancer with an ESR1 mutation are eligible to participate in the next round of Fablyn’s upcoming clinical trial.

An upcoming phase 3 clinical trial will compare the safety and efficacy of Fablyn (lasofoxifene) plus Verzenio (abemaciclib) to the standard treatment of Faslodex (fulvestrant) plus Verzenio in pre- and post-menopausal patients with locally advanced or metastatic ER+/HER2- breast cancer with an ESR1 mutation.

The randomized multicenter study will enroll 400 patients who have seen disease progression on either Ibrance (palbociclib) or Kisqali (ribociclib) as their first line of hormonal treatment for breast cancer. All patients must have hormone receptor-positive disease as well as the ESR1 mutation, or estrogen receptor gene mutation, which is frequently acquired during treatment and may lead to treatment resistance towards estrogen deprivation therapy.

Of note, Fablyn’s manufacturer Sermonix has paired with Guardant Health to test patients for trial eligibility using their Guardant360 CDx liquid biopsy, the first liquid biopsy with FDA approval.

“We are very pleased to partner with Sermonix on the continued development of (Fablyn), a promising investigational treatment for select metastatic breast cancer patients who are increasingly resistant to existing endocrine therapies,” Helmy Eltoukh of Guardant Health said in the press release. “The Guardant360 CDx test has played a key role in the pivotal trials of several recent precision cancer therapies, and we are excited to partner with Sermonix and support its efforts to address this important and underserved patient population.”

Patients receiving the experimental Fablyn treatment will receive oral doses of Fablyn and Verzenio twice daily, while those in the control group will receive Faslodex through an injection to a muscle on the first, 15th and 29th days of treatment before starting monthly injections as well as Verzenio by mouth twice daily.

The study is expected to begin in March of 2023 and end in June of 2026, and will evaluate progression-free survival (time from treatment until disease worsens) over the course of those three years. Other endpoints evaluated in this study include overall survival (time from treatment until death of any cause), overall response rate (percentage of patients whose disease shrinks as a result of treatment), quality of life, patient-reported outcomes on sexual health and duration of response, among others.

If Fablyn plus Verzenio can demonstrate a clinically significant improvement in these categories when compared to the patients treated with Faslodex and Verzenio, it may become the new standard of care in this patient population, according to the release.

“The initiation of this phase 3 combination study is a significant step forward for Sermonix, as we work to develop a novel targeted endocrine treatment option for metastatic breast cancer patients who are post-CDK4/6i with an ESR1 mutation and have limited treatment options that can provide meaningful clinical response,” said Dr. David Portman, founder and CEO of Sermonix. “We believe the inclusion of the Guardant360 CDx liquid biopsy to accurately identify eligible trial participants will enable us to execute this important study as efficiently as possible. We look forward to dosing the first patients very soon in this area of great unmet medical need.”


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