BOSTON (Reuters) — Two new drugs developed by Bayer AG, Onyx Pharmaceuticals Inc. and Pfizer Inc. help slow the growth of the most common form of kidney cancer, two studies published by the companies said on Wednesday.The biotech drugs, called Sutent and Nexavar, “are a major step forward in our struggle against kidney cancer,” said Dr. James Brugarolas of the University of Texas Southwestern Medical Center in Dallas.

“Both (drugs) delay the growth of kidney cancer by 3 to 6 months,” Brugarolas wrote in a commentary on the results, to be published in Thursday’s New England Journal of Medicine.

About 30,000 cases of renal cell carcinoma, involving the outer cells of the kidney, are diagnosed in the United States each year. It is responsible for up to 90 percent of all kidney cancers, and accounts for 1.5 percent of cancer deaths.

Patients typically survive for just a year.

Interleukin-2 and interferon alfa are often given to treat it. But they only work in about 5 percent of patients whose tumors have spread. Only interleukin is approved for that use in the United States.

In the test of sunitinib, a drug marketed under the brand name Sutent, the response rate was 31 percent versus a rate of 6 percent for treatment with interferon alfa, said the team led by Robert Motzer of the Memorial Sloan-Kettering Cancer Center in New York.

The 375 who received the Pfizer drug as part of the test involving researchers from the United States, France and Poland typically went for 11 months without having their tumour progress, compared to five months for an equal number of volunteers receiving interferon.

However, the drug also produced more side effects such as diarrhea and vomiting, and initial results showed no clear increase in survival.

Motzer called treatment with Sutent a new standard of care for advanced kidney cancer.

The test of sorafenib, sold as Nexavar, did not compare the drug to any established treatment. Half of the 903 volunteers in 19 countries received a placebo instead.

Response to the drug was so strong that the research team, headed by Bernard Escudier of the Gustave Roussy Institute in Villejuif, France, allowed placebo recipients to begin taking Nexavar.

While patients who received the placebo went an average of 2.8 months without their tumour progressing, the delay was 5.5 months for those getting Nexavar.

The drug affected the tumors of ten percent of the volunteers, compared with just 2 percent among placebo recipients.

But, once again, the initial results did not yet show that patients given the drug lived any longer, and Nexavar produced side effects such as skin problems and diarrhea.

Brugarolas said the side effects of both drugs can be severe in ten percent of patients. He said until the two drugs are compared in a head-to-head test, nobody will know which is better.

Both drugs work by inhibiting tumour growth and limiting the amount of blood going to a tumour.