(CNN) —  

Sheldon Adelson, a Las Vegas casino magnate and one of the Republican Party’s biggest donors, is undergoing treatment for cancer.

Adelson, 85, is dealing with “side effects from medication he is taking for the treatment of Non-Hodgkin’s lymphoma,” Las Vegas Sands spokesman Ron Reese said in a statement emailed to CNN and other news outlets. “These side effects have restricted his availability to travel or keep regular office hours.”

He said Adelson is still fulfilling his duties as chairman and CEO of Las Vegas Sands and is expected to resume a regular work schedule after he completes his treatment.

Adelson presides over a far-flung casino empire with opulent resorts in Las Vegas and a string of casinos in Macau, a Chinese gambling haven. He’s worth $36 billion, according to Forbes.

News of Adelson’s health first emerged during a court hearing this week about whether Adelson could sit for a deposition in long-running lawsuit. In that hearing, one of his attorneys, James Jimmerson, described Adelson’s health as “dire” and said CEO had not been seen in Sands corporate offices since Christmas. (The Nevada Independent first reported on Jimmerson’s comments to the court.)

Adelson and his wife, Miriam, are among the Republican Party’s largest donors. In the 2018 midterm elections alone, the couple contributed more than $122 million to Republican groups, according to a tally by the nonpartisan Center for Responsive Politics.

In the 2016 campaign, the Adelsons emerged as major financial supporters of Donald Trump’s presidential ambitions, donating $20 million to a pro-Trump super PAC. And Sheldon Adelson was the single largest individual contributor to Trump’s inaugural committee, giving $5 million.