While there were no issues of efficacy or safety behind a new US CRL for Daiichi Sankyo/Merck & Co's anti-HER3 antibody-drug conjugate patritumab, the FDA decision marks a hit to the companies' first ADC collaboration and the latest in a string of regulatory blows to Japanese firms in the US.

Failure of the EMBARK confirmatory trial convinced US FDA reviewers the Duchenne muscular dystrophy gene therapy did not show clinical benefit, but biologics center director Peter Marks invoked totality of evidence to grant full approval.

Several Japanese firms are facing R&D challenges and setbacks in the US, in the form of missed Phase III endpoints, trial recruitment difficulties and a Complete Response Letter.

With several new drugs progressing for the estimated 70,000 patients in China with DMD, a recent setback for Nippon Shinyaku's contender and progress for Chinese gene therapy developers are adding both uncertainty and likely competition in an untapped market with pressing medical need.