After a number of rounds through the courts, a Federal Appeals court upheld an earlier District Court judgement in favour of Genentech that all claims asserted by Chiron for alleged infringement of its patent for trastuzumab (Herceptin) are invalid.

In 2002, Chiron sued Genentech for patent infringement, alleging that it had invented a crucial technology (US Patent 6,054,561) used in creating the metastatic-breast-cancer blockbuster drug trastuzumab. The company claimed that it was entitled to as much as 30% of drug sales; however, a federal jury unanimously decided that Chiron had no claim to share any profits from trastuzumab, deciding that the US Patent and Trademark Office had improperly granted Chiron's patent.