The more and more research I do on cancer, I find that it's greatest correlation is chronic inflammation. So, there is a direct link between liver cancer and hepatitis (whether caused by drinking aka cirrhosis, drug induced, viral, etc). I'm sure this would be the case with chronic use of Tylenol. Plus, most conditions where long-term tylenol use is required, are prescribed much higher dosages that 100mg. I'm talking prescriptions of 1000-5000 daily (mind you 5000mg is the lowest threshold and is rare). I'm sure that the chronic inflammation from such a regiment would greatly increase one's chance of not only liver failure, but liver cancer as well.
I'm sure this would be the case with GW. Lower dosages have been taken in studies daily for up to two years in clinical trials with minimal to no side effects and zero instances of cancer related conditions. Now these dosages are half of what has been considered a good bodybuilding dose (1-5mg vs 10-20mg), but are still fairly close to one another and much lower than the equivalent doses shown to produce cancer (300-500mg). Mind you that these high doses where also run for a fairly significant amount of time (I can't remember the exact numbers off the top of my head though). With that said, these "bodybuilding" doses have been shown to be very effective in short periods of time comparatively (8-12 weeks). If one were to use these dosages over that time frame with a relatively high amount of time between runs say a 2:1 ratio, I honestly don't see how it could be anymore detrimental than the lower dosages taken for years at a time.
Now, this is with my minimal training on drug administration (a couple semesters in college), but I think it is consistent with the theory I learned back then. My opinion of the WHO is that they are very reactionary and easily swayed by political and popular thinking. I take their opinion with a grain of salt when I read articles like the one previously quoted. And honestly, I think that the main reason the drug company that was running the studies abandoned the clinical trials was more due to public opinion of cancer, public limelight of the study, and fear of litigation rather than a true safety concern. There have been many other drugs for various conditions that have been made publicly available with a much higher instance of negative and potentially fatal side effects at recommended doses than what had been demonstrated with GW.