Based on this[0], it's roughly an increase from about 0.02% chance to about 0.034% chance (given no other information to base your risk on)
The main risk seems to be going from "so slow growing you die of old age first" to "fast enough growing it becomes a problem", unless I am horribly mistaken.
I don't know how representative the samples were of the entire population - one theory was that our young motorcycle samples had significantly higher testosterone on average and were more likely to develop those tumors.
>This was a large, well designed study that supports previous research linking high blood levels of omega-3 fatty acids with prostate cancer risk. However, it cannot show that fish oil supplements cause prostate cancer and it is possible that other confounders affected men’s risk (although the researchers tried to take these into account).
Their conclusion contradicts their own headline.
Headline says there is some correlation between the two but they are careful to explain later that this does not necessarily imply causation and that further research is required.
"Still, it is unlikely that the high levels of these fatty acids found in the highest quartile would be the result of diet alone. Adults are advised to eat two portions of fish a week, one of them oily, as part of a healthy balanced diet."
You are right that the study doesn't explicitly say fish oil supplements directly caused the high levels of fish oil which were observed in these patients with prostate cancer.
Dailymail at it again :).