Maybe they were referring to something along the lines of this? (Note: I have not seen the study referenced in my linked article, and cannot vouch for the accuracy of Flux's statement)

http://www.health.harvard.edu/staying-healthy/blue-light-has...

"But we do know that exposure to light suppresses the secretion of melatonin, a hormone that influences circadian rhythms, and there’s some experimental evidence (it’s very preliminary) that lower melatonin levels might explain the association with cancer."

People that work night shifts are at higher risk of getting cancer.

http://jnci.oxfordjournals.org/content/93/20/1563.full

This has been known for quite some time, amongst the contributing factors considered there's also light exposure during "dark hours", especially when it comes to cold (blue) lighting.

Well prevent might be a big word :) Reduces change because you should sleep more with f.lux. And that should reduce your chance for cancer.

No mention of prevention