Former Senate Majority Leader George Mitchell, who's leading the investigation into steroid use by baseball players, has been diagnosed with prostate cancer, according to his law firm.

"The cancer is small, low grade, and localized, and can be effectively treated and cured," Mitchell's doctor Harvey Klein said in a statement released by the firm. "The prognosis is very good."

Mitchell, 73, said the diagnosis and treatment will not affect his baseball probe.

"The investigation, which is in its final phases, will be completed in the coming months and neither the substance nor the timing of the report will be affected in any way," he said in the release.

The former federal judge and prosecutor was hired by baseball commissioner Bud Selig in March 2006 to look into performance enhancing substances. Mitchell has not publicly stated a timetable for issuing his report.

The Maine Democrat entered the Senate in 1980 and rose to become majority leader in 1989. After leaving the Senate in 1995, he helped broker peace in Northern Ireland and investigated violence in the Middle East.

Now a New York resident, Mitchell is chairman of DLA Piper law firm