Shares of Zymeworks and Jazz Pharmaceuticals climbed after the companies released what they called positive topline results from a late-stage trial of their treatment for certain cancers, including of the stomach, gastroesophageal junction and esophagus.

Zymeworks' stock rose 36%, to $25.17, in premarket trading Monday, while Jazz Pharmaceuticals' stock gained 22%, to $171.7. Through Friday's close, shares of Zymeworks are up nearly 27% so far this year, and shares of Jazz Pharmaceuticals are up nearly 15%.

The companies said before the bell that the safety profile of their treatment, zanidatamab-hrii, used in combination with chemotherapy as a first-line treatment for HER2-positive locally advanced or metastatic gastroesophageal adenocarcinoma was generally consistent with the known safety profile of each agent. The recent trial results support the overall benefit-risk of the drug for use in this indication, the companies added.

The companies expect to submit a supplemental biologics license application in the first half of 2026 to support zanidatamab-hrii as a first-line treatment. The treatment is currently approved in the U.S., Europe and China for use in second-line biliary tract cancer and is marketed under the trade name Ziihera.

BeOne Medicines is helping to develop and commercialize the treatment.