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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Political parties across the country suspended their General Election campaigns following the Manchester Arena terror attack on Monday.
Investigators believe Mr Kushner has significant information relevant to their inquiry, officials told NBC News.
The men were detained as part of an investigation by MI5 and the Metropolitan Police's Counter Terrorism Command.