WASHINGTON, Feb 25 (Reuters) - The U.S. Food and Drug Administration said on Monday it has approved Bayer AG's drug Stivarga for the treatment of a rare type of gastrointestinal tract cancer. Stivarga is already approved to treat colon cancer that has progressed after prior treatment or that has spread to other parts of the body. Bayer will now also be able to market the drug as a treatment for gastrointestinal stromal tumors (GIST). Stivarga, known chemically as regorafenib, was tested in 199 patients with GIST that could not be surgically removed and had progressed after treatment with Novartis AG's Gleevec and Pfizer Inc's Sutent. Patients taking Stivarga had a delay in tumor growth progression of 4.8 months, compared with 0.9 months for patients in the placebo group. Shannon Campbell, vice president and general manager of Bayer's oncology business, said in a telephone interview that the drug will be priced on a par with the $9,350 per 28-day cycle of treatment set for the drug's use in colon cancer. Under an agreement signed in 2011, Onyx Pharmaceuticals Inc will receive a 20 percent royalty payment on global sales of Stivarga. The agreement followed a dispute over how closely related the treatment is to Nexavar, a kidney and liver cancer drug that the companies co-developed. Bayer and Onyx will jointly market Stivarga in the United States. Bayer will market it alone in the rest of the world. Stivarga is a pill that works by blocking several enzymes that promote cancer growth.