UPDATE 1-US FDA backs Roche's Herceptin in stomach cancer

* Herceptin prolongs lives of stomach cancer patients

* Approved by European regulators in January

LOS ANGELES Oct 20 (Reuters) - Roche Holding AG's (ROG.VX) cancer drug Herceptin has been approved, in combination with chemotherapy, by U.S. regulators as a treatment for patients with HER2-positive advanced stomach cancer, the company's Genentech unit said on Wednesday.

Herceptin, or trastuzumab, is already approved for use in the 25 percent or so of breast cancer patients whose tumors generate the HER-2 protein, which can fuel cancer growth.

The latest FDA approval is based on a pivotal trial which showed that people who received Herceptin plus chemotherapy lived longer compared to those who received chemotherapy alone.

European regulators approved Herceptin for stomach cancer in January.

According to the American Cancer Society, an estimated 21,000 Americans will be diagnosed with stomach cancer and more than 10,500 will die from the disease in 2010. More than 64,000 Americans are currently living with the disease.

(Reporting by Deena Beasley; Editing by Bernard Orr)