The 63-year-old broadcaster will remain on BBC News At Six as much as he can, but may need to reduce his appearances over the coming weeks.
George previously underwent 17 rounds of chemotherapy to treat advanced bowel cancer in 2014, before returning to presenting duties in 2015.
However, in January 2018 he disclosed that the cancer had returned.
His agent Mary Greenham told the Press Association: “George Alagiah will aim to be on air as much as possible, but may need to reduce his workload in the next few weeks as he begins a new regime of treatment to deal with a recent recurrence of his cancer.
“He is always grateful to the public for the tremendous support he has received.”
George, who has presented BBC News At Six for more than 10 years, returned to the BBC newsroom in January this year for the first time since December 2017.
Earlier this year, the Sri Lanka-born newsreader hosted a Bowel Cancer UK podcast, in which he spoke candidly about his treatment and living with the disease.
“I had a stoma, but I didn’t look disabled,” he explained. “And I would be turning the key at a disabled loo at the motorway service station and if there was a queue and somebody obviously disabled, I used to feel guilty and like I needed to apologise and explain.”