> One further patient, identified only as Drew, has been tumour-free for over four years after receiving immunotherapy.
The key part of the article, in my opinion, is this one (referring to the 13 year old):
> The scientific teams at Gustave Roussy cancer centre in France are now working intensively to understand what made his response possible. Their current hypothesis centres on what Dr Grill described as an extremely rare mutation in Lucas's tumour cells that made them unusually sensitive to everolimus by creating a dependency on the mTOR pathway. Researchers have begun creating tumour organoids, three-dimensional laboratory-grown models that mirror each patient's tumour's genetic characteristics, to test whether Lucas's specific cellular profile can be replicated.