CHICAGO -- Conservative political commentator Robert Novak announced his immediate retirement Monday because of his diagnosis of a malignant brain tumor.

Novak told the editor and publisher of the Chicago Sun-Times that he plans to focus on his treatment and recovery, said Sun-Times spokeswoman Tammy Chase.

Novak told the newspaper his prognosis is “dire,” the Sun-Times reported on its Web site.

“The details are being worked out with the doctors this week, but the tentative plan is for radiation and chemotherapy,” Novak said.

Chase confirmed Monday that Novak’s tumor is malignant. He was discharged from Brigham and Women’s Hospital in Boston on Saturday, said Kevin Myron, a hospital spokesman.

Novak announced that he had a brain tumor late last month, less than a week after he struck a pedestrian with his Corvette in downtown Washington and drove away. He received a $50 citation for the accident.

Novak, editor of the Evans-Novak Political Report, has been a columnist for the Chicago Sun-Times for decades. He is perhaps best known as the longtime co-host of CNN’s “Crossfire” from 1980 to 2005.