Sen. Tom Coburn (R-Okla.) has been diagnosed with a recurrence of prostate cancer and is undergoing treatment, his spokesman confirmed Tuesday.

Coburn, 65, was previously treated for prostate cancer in 2011 and has also undergone treatment for colon cancer and melanoma.

Coburn spokesman John Hart said he hopes the senator will return as early as next week.

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Coburn, a former member of the U.S. House who first ran for the Senate in 2004, also was treated for malignant melanoma in 1975, and had a benign tumor removed from his pituitary gland in 2007. He also was tested for an irregular heartbeat in 2008.

Earlier this month, Coburn was among a group of senators who released the findings of a two-year probe into alleged abuses in how Social Security disability benefits were approved at a federal Office of Disability Adjudication and Review in West Virginia.

Coburn’s fellow U.S. senator from Oklahoma, Jim Inhofe, underwent emergency quadruple bypass surgery in Tulsa last month. Two of Inhofe’s arteries were completely blocked, another was at 90 percent blocked and a fourth was 75 percent blocked.

Inhofe’s campaign manager said Tuesday that the 79-year-old senator spent his first day back in Washington on Monday.

Updated at 5:47 p.m.