First off, I think the term "man-made" in this context is highly misleading. In this context, I think most people would see that headline and think it means cancer was designed and manufactured by humans. Sounds like a conspiracy theory, similar to HIV being made for nefarious purposes. Perhaps a re-wording is needed, like "Researchers finally confirm that cancer is far more due to human-caused external factors than previously thought."

Like you, I thought this was a no-brainer to begin with. One thing not addressed in this article is exposure to nuclear radiation.