St. John the Baptist Parish District Attorney Tom Daley said Saturday that he is withdrawing from a Dec. 6 runoff, in which he was seeking a second six-year term, because his cancer has returned, effectively electing an assistant who was slated to square off against him in the runoff.

Daley, 61, captured 46.3 percent of the vote in Tuesday’s three-candidate primary, falling short of the majority needed to avoid a runoff. His departure from the campaign means that Bridget Dinvaut, an assistant district attorney in Daley’s office who finished second with 34.3 percent, will be sworn in next year as district attorney.

Daley underwent surgery last year to remove a brain tumor. He said during the campaign that he had been given a clean bill of health, indicating no new issues.

That changed Friday after a follow-up visit with his neurosurgeon, who “advised me in very strong terms that he felt that my brain cancer was beginning to grow, and he recommended in very strong terms that I cease and desist my campaign activities,” Daley said by phone Saturday.

“He told me … that it was his medical recommendation that I cease campaigning and that I spend some time with my family, that I take my tie off and put on a pair of blue jeans and use my time wisely.”

Daley had undergone chemotherapy treatment for most of the past year, and he recently applied to participate in a clinical trial for a new medicine but was not accepted. He said he will find out next month if he has to undergo another surgical procedure.

Stepping aside from the race was the right decision, he said, though he intends to serve out his term, which ends early next year. Daley plans to notify the Secretary of State’s Office of his decision on Monday.

“I think I could win the election, but I didn’t want to win the election, take office and a year into the six-year term, I’d have to resign or step down for health reasons and then we’d have to have another election,” he said. “I thought that would be very counterproductive.”

After getting the news from his doctor, Daley said he had “a very good meeting” with Dinvaut on Friday to inform her of his decision. “I feel very positive that I’ll be able to work with her,” he said. “Together, we will assure that there will be a smooth, professional transition in the office.”

Daley, who lives in LaPlace, spent 18 years as a judge on the Louisiana 5th Circuit Court of Appeal and the 40th Judicial District Court before his 2008 election. He posted a letter about his new diagnosis Friday night on his Facebook page, which drew a steady stream of well-wishes and comments from residents thanking him for his years of service.

Before she took a leave of absence to campaign, Dinvaut, 52, had worked for Daley as an assistant district attorney since 2010 while also maintaining a private legal practice in LaPlace that focuses mostly on employment law.

Dinvaut, a Democrat, graduated from Southern University at New Orleans and received her law degree from the Southern University Law Center.

During the campaign, she said her extensive law enforcement background gave her “a proven record as a crime fighter.” She worked in the St. John Parish Sheriff’s Office from 1986 until 1994, then spent eight years as a federal law enforcement officer in Louisiana and Florida. In 2005, she began practicing law at the New Orleans-based firm of Lemle & Kelleher before joining Daley’s office in 2010.

Daley said he has been feeling mostly fine lately, though more tired than usual, which he said is natural after the stress of a campaign. He said he had been ready for the grind of a second term, but the meeting with his doctor put things in a different perspective.

“I’m 12 months into this cancer treatment, so I’m not naive about it,” he said. “Sometimes you can cloud yourself with regard to that.”

Follow Richard Thompson on Twitter, @rthompsonMSY.