UPDATE 1-Roche's Herceptin prolongs stomach cancer survival

* Positive results in late-stage trial

* Herceptin already approved in breast cancer

(Adds details)

ZURICH, March 18 (Reuters) - Roche Holding AG's (ROG.VX) Herceptin significantly prolonged the lives of patients with advanced stomach cancer in a late-stage trial, the Swiss drugmaker said on Wednesday.

Nearly 600 patients with HER2-positive stomach cancer were enrolled in the trial, which showed that adding Herceptin to standard chemotherapy extended survival.

Herceptin is approved to treat breast cancer and its use against stomach cancer is being evaluated. (Reporting by Sam Cage; Editing by Hans Peters)