These oversimplified analyses are rampant among researchers. Why do they even release this information? Isolate the generic term "fish oils" and throw in "increase cancer risk" without actually stating very detailed data obscures the truth.
What brand of fish oils were used? Dosages? Contaminants? Diets of participants? Lifestyles? etc. etc.. etc...
Why do I have a feeling they uses statistics to come to this conclusion?
Anyway, taking an isolate that may become rancid will definitely be different than eating fish as a whole.