April 14 (Bloomberg) -- Pfizer Inc.'s Sutent, a drug for kidney tumors, slowed the spread of an aggressive form of liver cancer in a small clinical trial.

A study of 34 patients with an inoperable form of hepatocellular carcinoma found one patient had partial tumor shrinkage and 17 others had their tumors stabilize, researchers said today at a medical meeting in San Diego. Patients taking Sutent lived for a median time of 10 months, researchers said.

The benefit appears similar to that seen from a competing medicine, Onyx Pharmaceuticals Inc. and Bayer AG's Nexavar, which is approved to treat kidney and liver cancers. Nexavar is the first medicine shown to extend lives for people with liver tumors. An estimated 21,000 people will be diagnosed with cancer of the liver or bile duct this year, and more than 18,000 will die from it, according to the Atlanta-based American Cancer Society.

``Results are still preliminary, but there is clear evidence of an anti-tumor activity in these patients,'' said Andrew Zhu, director of liver cancer research at Massachusetts General Hospital in Boston, in a statement.

The data was reported today in a plenary presentation at the American Association for Cancer Research meeting in San Diego.

About 18 percent of patients on Sutent reported high levels of a liver enzyme in the blood, a sign of liver injury. About 12 percent of patients had their infection-fighting white blood cells significantly depleted while on therapy, and the same number reported a drop in platelet cells in the blood, which help with clotting.

Vessel Blocker

Like Nexavar, Sutent is designed to work by blocking a protein that leads to blood vessel formation and others involved in tumor proliferation, researchers said. It is thought to be a good candidate for treating liver cancer because the disease relies heavily on blood vessels for growth, Zhu said.

Sutent, first approved in January 2006 for kidney cancer, generated $581 million in sales in 2007, New York-based Pfizer has said. It also won approval for gastrointestinal stromal tumors, known as GIST.

Pfizer rose 11 cents, or less than 1 percent, to $20.56 at 4 p.m. in New York Stock Exchange composite trading. The stock has dropped 23 percent in the past year.

Nexavar was approved by U.S. regulators in November 2007 for liver cancer, after a clinical trial showed it helped patients live a median of 10.7 months, compared with 7.9 months for patients on a placebo. It was originally cleared for sale in December 2005 for kidney tumors.

Liver cancer is associated with Hepatitis B and C infection, and alcoholism, researchers say. More people may get the disease in the future because studies show obesity may play a role, said Ghassan Abou-Alfa, a liver cancer specialist at Memorial Sloan- Kettering Cancer Center in New York.

To contact the reporter on this story: Luke Timmerman in San Francisco at ltimmerman@bloomberg.net

Last Updated: April 14, 2008 17:26 EDT