Sally Roberts has exclusively told ITV Daybreak that she is concerned that radiotherapy treatment could be damaging to her son Neon, by affecting his DNA.
She said there are "so many" other treatments that her son could be having instead.
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He has asked his followers for help in tracking the man down.
The president said it was a “very sad day for journalism”.
A summit has been pencilled in for February following last year’s icebreaker in Singapore.