Coburn, 59, is expected to have a complete recovery from Wednesday's surgery and may return to his Senate work by the end of this month, spokesman John Hart said.
Coburn, a physician, went to the Mayo Clinic because it specializes in pituitary tumors, Hart said.
The condition was unrelated to two other cancers that Coburn has overcome. Coburn had colon cancer in 2003 and a malignant melanoma in 1975.
Coburn, R-Muskogee, was elected to the U.S. Senate in 2004; he served in the U.S. House from 1995 to 2001.
