Former state Assemblyman Ira Ruskin, whose district included Menlo Park, Atherton, Woodside and Portola Valley, has been diagnosed with a brain tumor and is halting his political career.

Mr. Ruskin, a Democrat from Redwood City, told his supporters in an email Thursday that he had undergone emergency surgery for a malignant brain tumor about two weeks ago and that he is preparing to undergo "aggressive treatment," including radiation and chemotherapy.

Mr. Ruskin, 67, said he was advised by his doctors that the tumor, while not curable, is containable.

"The surgery went well, and my recovery has been great," Ruskin wrote. "I feel so improved and reinvigorated."

He was elected to the State Assembly in 2004, when he defeated Republican Steve Poizner to succeed former Palo Alto Mayor Joe Simitian. He was easily re-elected twice before being termed out in 2010. He was succeeded by fellow Democrat Rich Gordon.

The 21st District straddles Santa Clara and San Mateo counties and includes Menlo Park, Atherton, Woodside, East Palo Alto, Redwood City, San Carlos, Palo Alto, Los Altos, Stanford, and a small part of San Jose.

Mr. Ruskin and Sen. Simitian both made appearances at Mr. Gordon's celebration party on Election Night. At that time, Mr. Ruskin told the audience that he planned to run for Sen. Simitian's seat in the state Senate in 2012.

Now, he is putting these plans on hold to focus on recovery, he wrote.

"Given the treatment ahead, I am withdrawing from all political activity at this time in order to focus on my recovery and to be with my wife, Cheryl, friends, and family," he wrote. "I will be looking inside myself to understand how I want to spend my time and how I otherwise want to contribute to the community."

Mr. Gordon released a statement Friday morning praising Mr. Ruskin's service in the Assembly. He said he has been "impressed by the deep respect that so many in Sacramento have for Ira."

"He obviously did an outstanding job in the State Assembly," Mr. Gordon said. "I wish Ira the best and my thoughts will be with him in the days ahead."