Blues point about EPO enhancing cancer may have some value because cells do better with a better oxygen supply. Duh! Do you really want to provide better oxygenation to fast proliferating cells? Treatments are moving in the opposite direction - http://www.news.cornell.edu/stories/Feb ... 91.kr.html
HOWEVER, despite the seeming logic, gh's point remains valid. You would expect that cancer in EPO endurance athletes would be observable earlier and advance more quickly compared to a normal population but if there is no evidence of actual outcomes like this then the logic doesn't matter, irrespective of how seductive it might be.
Given that EPO has been used by likely tens of thousands of athletes over about 20 years there should have been some indication although you may not see much effect given that the age cohort of EPO users is not very cancer prone.