Menarini Orserdu Initiates Phase 2 Bridging Trial in Japan for PMDA Submission
70-Patient Bridging Study Targeting Japanese Approval
Stemline Therapeutics, a wholly owned subsidiary of the Menarini Group, has initiated the Phase 2 bridging trial NCT07766018 for Orserdu (elacestrant) monotherapy in Japan. This multicenter, open-label, single-arm trial will enroll 70 postmenopausal Japanese women and adult men and is currently recruiting at Tokai University Hospital as of August 2026. The primary goal is to replicate the global evidence obtained in the U.S. and Europe in the Japanese patient population to build the efficacy and safety data required for review by the Pharmaceuticals and Medical Devices Agency (PMDA).
Directly Targeting ESR1-Mutant Resistance
Orserdu is an oral selective estrogen receptor degrader (SERD) that blocks and degrades estrogen receptors (ER), with the target molecule being ERα encoded by ESR1. The trial targets patients with ER-positive, HER2-negative advanced or metastatic breast cancer who have ESR1 mutations detected via Guardant360 CDx and have progressed after 1–2 lines of endocrine therapy for metastatic disease, including CDK4/6 inhibitors combined with fulvestrant or aromatase inhibitors. Therefore, this trial is aimed at the molecularly selected subsequent treatment market following therapies such as Ibrance (palbociclib), Kisqali (ribociclib), and Verzenio (abemaciclib).
U.S. and EU Approval Rationale Already Established
The FDA approved Orserdu for the ESR1-mutant indication on January 27, 2023, and also approved Guardant360 CDx as a companion diagnostic, without requiring external advisory input or referring it to the Oncology Drug Advisory Committee (AdComm). The European Union Executive Committee granted approval on September 15, 2023, based on the Phase 3 EMERALD trial, which compared elacestrant with fulvestrant or aromatase inhibitors in 228 ESR1-mutant patients out of 478. The Japanese Phase 2 trial is more of a regional regulatory expansion for an already approved drug rather than a new global confirmatory trial, but the consistency of data from the single-arm 70-patient study directly impacts the PMDA submission strategy and local commercialization timeline.
Competitive Advantage Is No Longer Exclusive
Beyond standard endocrine therapies such as fulvestrant and aromatase inhibitors, Eli Lilly’s Inluriyo (elinerestrant) received FDA approval on September 25, 2025, and Arvinas and Pfizer’s Veppanu (bardoxolone) received approval on May 1, 2026, expanding treatment options in the ESR1-mutant market. AstraZeneca’s camizestrant is undergoing FDA AdComm review in April 2026 based on the Phase 3 SERENA-6 trial, and Roche Holding’s giredestrant is also in Phase 3 development. The Japanese breast cancer treatment market is projected to grow from $475.6 million in 2023 to $795.4 million in 2030, making regulatory approval speed, companion diagnostic accessibility, and prescribing positioning relative to competing drugs increasingly important for Menarini.
In the short term, the speed of enrolling 70 patients and the consistency of efficacy and safety data in Japanese ESR1-mutant patients will determine the PMDA submission timeline. The Japanese breast cancer treatment market is expected to expand from $475.6 million in 2023 to $795.4 million in 2030, so approval could broaden Menarini’s revenue base in Asia. However, Orserdu will face competition from Inluriyo and Veppanu in the commercial phase and from camizestrant and giredestrant in later development stages. For researchers, patient selection based on CDK4/6 inhibitor failure and Guardant360 CDx, along with data on oral ER degraders in the Japanese population, represent key value propositions. Mid- to long-term investment decisions should consider Japan regulatory progress, local reimbursement conditions, and milestone and royalty obligations under the 2020 licensing agreement.
Source: ClinicalTrials.gov (api_ct)