From the article:
“Stem cells use ascorbate to regulate the abundance of certain chemical modifications on DNA, which are part of the epigenome,” said Dr. Michalis Agathocleous, lead author of the study. […] “The epigenome is a set of mechanisms inside a cell that regulates which genes turn on and turn off. So when stem cells don’t receive enough vitamin C, the epigenome can become damaged in a way that increases stem cell function but also increases the risk of leukemia.”
This increased risk is partly tied to how ascorbate affects an enzyme known as Tet2, the study showed. Mutations that inactivate Tet2 are an early step in the formation of leukemia.