The Food and Drug Administration has approved a new treatment for an advanced form of kidney cancer, the agency announced Tuesday.

In trials, kidney cancer patients treated with Nexavar, also known as sorafenib toylate, went longer without their cancer progressing than those taking a placebo. The drug was developed by Bayer and Onyx Pharmaceuticals.

The medicine is for patients with advanced renal cell carcinoma, the most common type of kidney cancer. According to the FDA, in one trial, patients taking the drug went twice as long — six months vs. three months for those taking a placebo — without the cancer progressing or the patient dying.

The companies said people taking the drug also lived longer, although FDA officials said it was too soon to say conclusively that was the case.

"We believe this represents, from a medical point of view, truly a major advance," Dr. Richard Pazdur, director of FDA's Office of Oncology Drug Products, said in a conference call with reporters.

"Rarely do we see a 100 percent improvement" in a new cancer treatment, Pazdur said.

About 12,000 Americans die of kidney cancer every year, and 32,000 new cases are diagnosed, accounting for 3 percent of all adult cancers. It occurs most often in people aged 50 to 70, twice as often in men than in women. If the cancer is detected early, it can be cured with surgery.

Nexavar, taken orally, works by targeting a tumor's blood supply and growth, the developers said in a statement. The drug is being studied to see if it inhibits other kinds of cancer.

It is the first kidney cancer treatment approved in more than a decade, the companies said. It will be available almost immediately.

About 40 percent of the people taking the drug had diarrhea and other gastrointestinal side effects, but FDA officials said the drug had fewer toxic side effects than other cancer treatments. Other side effects include rash, increased blood pressure, and blisters on the palms of the hands or soles of the feet.