The 62-year-old presenter of the BBC News at Six was previously diagnosed with bowel cancer in 2014, which later spread to his liver and lymph nodes.
He returned to work in November 2015 after being cleared of the disease following extensive treatment. But in a statement Alagiah’s agent, Mary Greenham, said the disease had recurred. She said Alagiah, a father of two, was in discussions with doctors about options for treatment.
Alagiah spoke of his determination to fight the disease for a second time. “My brilliant doctors are determined to get me back to a disease-free state and I know they have the skill to do just that,” he said.
“I learned last time around how important the support of family and friends is and I am blessed in that department. I genuinely feel positive as I prepare for this new challenge.”
The Sri-Lanka-born presenter first informed his doctors of a problem in 2014. After a colonoscopy, a tumour was discovered on his bowel.
MRI scans later detected eight tumours in his liver. He had several rounds of chemotherapy and three major operations, one of which included the removal of most of his liver.
He has spoken frankly about the chances of the disease recurring. In 2016 he told the Telegraph: “I get anxious and then there is a huge relief when the doctor tells me it is clear again. But I am under no illusions.
“The doctor warned me last year: ‘Your cancer knows the road, the pathway out of the gut.’ It can happen again.”
Alagiah joined the BBC in 1989 and spent many years as one of the corporation’s leading foreign correspondents before moving to presenting the News at Six in 2007.
Last year the publication of a list of the best-paid on-screen staff at the corporation revealed he was paid between £250,000 and £299,999, putting him 25th in the table and making him the highest earner from a black or minority ethnic background.
A BBC spokesman said: “Everyone at the BBC sends George and his family their best wishes as he undergoes treatment and we will be thinking of them.”