Complete response letter outlines FDA’s request for additional information

NIJMEGEN, The Netherlands I May 15, 2023 I Byondis B.V., an independent, Dutch clinical-stage biopharmaceutical company creating precision medicines, today announced that the U.S. Food and Drug Administration (FDA) has issued a complete response letter (CRL) for the Biological License Application (BLA) for [vic-]trastuzumab duocarmazine (SYD985). With this BLA, Byondis sought approval for its anti-HER2 antibody-drug conjugate (ADC) in HER2-positive unresectable locally advanced or metastatic breast cancer (MBC), a disease with a high unmet medical need.

According to the complete response letter, the FDA suspends the decision on the product’s approvability. The agency requested additional information that requires time and resources that extend beyond the current evaluation period.

While Byondis is disappointed with this outcome, the company remains optimistic about SYD985’s potential. “We continue to believe that SYD985 can present a meaningful treatment option for patients living with HER2-positive metastatic breast cancer,” said Byondis CEO Marco Timmers, Ph.D. “We appreciate the FDA’s guidance and support and will carefully evaluate the complete response letter and consider potential next steps.”

Timmers added, “We will continue with the SYD985 applications in EU and UK and await the outcome of the review process.”

[Vic-]Trastuzumab Duocarmazine Phase III TULIP® Study Results
The BLA and MAA are supported by data from the pivotal Phase III TULIP multi-center, open-label, randomized clinical trial comparing SYD985 to physician’s choice (PC) treatment in patients with pre-treated HER2-positive unresectable locally advanced or metastatic breast cancer (SYD985.002/NCT03262935). The study, the results of which were presented at the 2021 ESMO Congress, met its primary endpoint of progression-free survival (PFS), demonstrating a statistically significant improvement of 2.1 months over PC. TULIP also demonstrated supportive overall survival (OS) results.

About Byondis
Driven to improve patients’ lives, Byondis is a privately held, Dutch clinical-stage biopharmaceutical research and development company creating precision medicines targeting intractable cancers and autoimmune diseases. Byondis’ broad development portfolio comprises targeted and immuno-oncology (IO) therapies in preclinical and early- and late-stage clinical phases. These candidates combine Byondis’ expertise in linker-drug (LD) technology, antibody-drug conjugation, targeted cytotoxic therapy, and monoclonal antibody (mAb) development. Byondis designs and produces next generation antibody-drug conjugates (ADCs), as well as mAbs and new chemical entities (NCEs) that can stand alone or be incorporated in its ADCs.

Byondis has a dedicated team of more than 400 employees, including highly educated scientists and skilled technicians working in state-of-the-art R&D laboratories and Good Manufacturing Practice (GMP) production and conjugation facilities on its campus in Nijmegen, the Netherlands. The company collaborates with other global biotechnology and pharmaceutical companies and many leading academic research institutions. For more information, visit

SOURCE: Byondis