A Pfizer Inc. kidney cancer drug has also shown promise in a small mid-stage trial as a treatment for the most common form of lung cancer, researchers said on Saturday.

The new study involved 63 patients whose non-small cell lung cancer had progressed despite earlier treatments with standard chemotherapy. All patients were then given Pfizer’s once-daily pill, Sutent, as a stand-alone treatment and continued to take it until their disease progressed.

Tumors shrank by at least 50 percent in six, or 9.5 percent, of the patients. They stopped growing in another 27, or 43 percent, of the patients, researchers said at the annual meeting of the American Society of Clinical Oncology being held in Atlanta.

Sutent was generally well tolerated, researchers said, with mostly mild to moderate side effects such as fatigue, nausea and shortness of breath.

Its effectiveness was comparable to that seen in separate earlier mid-stage trials of OSI Pharmaceuticals Inc’s Tarceva, a pill that had also been tested by itself among a similar group of lung cancer patients, said Dr. Bruce Johnson, director of thoracic oncology at the Dana Farber Cancer Institute.

“Both of these agents seem able to stabilize tumors and prevent them from growing,” said Johnson, who did not conduct the Sutent trial but was chosen to help explain its findings.

Johnson said Sutent’s ability to arrest tumor growth suggests it may prove able in larger trials to actually prolong lives of lung cancer patients, as Tarceva went on to do in its own late-stage trials that helped it win approval as a lung cancer treatment in the United States.

Both drugs block specific proteins that allow tumor cells to grow, and therefore cause far milder side effects than standard cancer treatments that also harm healthy tissue as they go after tumor cells.

“Any time you have well-tolerated agents like Tarceva and Sutent that can shrink tumors by themselves, they become candidates for use with standard chemotherapy,” Johnson said, a big potential use of the two medicines.

U.S. regulators in January approved Sutent, whose chemical name is sunitinib, to treat kidney cancer as well as a rare stomach and intestinal cancer known as GIST.

Larger trials will be needed to conclusively establish Sutent’s effectiveness against lung cancer, the most common cause of death from cancer in both men and women.

Cigarette smoking is the main cause of about 90 percent of lung cancer cases in men and about 70 percent of cases in women, according to the Merck Manual.