Genentech said it warned seven Japanese firms.

The U.S. biotechnology firm has warned seven Japanese companies to stop developing one of its drugs in what analysts describe as the start of the first biotechnology patent battle in Japan. Genentech’s lawyer in Tokyo said the company had sent letters to the pharmaceutical firms claiming priority over mass-production genetic engineering technology for the drug, tissue plasminogen activator. The lawyer said the South San Francisco-based firm had filed for a patent in Japan. The letter was required to protect the pending patent.