Byondis' breast cancer drug fails to bloom as FDA denies approval

Byondis' efforts to get an antibody-drug conjugate (ADC) treatment for HER-2 positive metastatic breast cancer approved have been pruned by the FDA. 

Last July, the federal agency accepted the Dutch company’s application for trastuzumab duocarmazine, also known as SYD985, an anti-HER2 ADC designed to treat HER2-positive unresectable locally advanced or metastatic breast cancer. The FDA set an expected decision date for May 12.

Now, the agency has rejected the drug in a complete response letter, saying that further unspecified information is needed, according to the biotech's Monday release. Byondis said the request would require time and resources “that extend beyond the current evaluation period,” according to a company release.

The biotech expressed disappointment but plans to continue seeking approval of the lead asset in the EU and the U.K.  

"We continue to believe that SYD985 can present a meaningful treatment option for patients living with HER2-positive metastatic breast cancer," Byondis CEO Marco Timmers, Ph.D., said in a May 15 release. "We appreciate the FDA's guidance and support and will carefully evaluate the complete response letter and consider potential next steps."

SYD985 was assessed in a multicenter, open-label, randomized phase 3 trial dubbed TULIP. The study showed a statistically significant improvement over a physician's choice of treatment among 436 patients with pretreated HER2-positive unresectable locally advanced or metastatic breast cancer, according to Byondis.

The asset—which received fast-track designation from the FDA in 2018—contains the monoclonal antibody Herceptin and an investigational cleavable linker drug, which can help boost the success of ADC therapies by making tumor cells selectively release the toxin in the therapy.  

Byondis is trying to enter a tight market dominated by Big Pharma. In the physicians' choice trial, SYD985 was evaluated against GSK’s Tykerb, Genentech’s Xeloda, Eisai’s Halaven, Roche’s Herceptin and the chemotherapy Navelbine. 

The company is also testing out SYD985 in patients with endometrial cancer, efforts that are currently in phase 2 development.