This is a common sleight of hand in the pharma (or general 'sickness industry') sponsored mercenary pseudo-science, when they want to "prove" that inexpensive, non-patentable substance X which is actually good for you, "causes" cancer -- they give X to mice bred specifically to develop cancers they wish to blame on X. After the coarse grained form of the "discovery" story is retold in mass media (or on Slashdot), it becomes "X causes cancer."
To see exactly how this sleight of hand works, consider substance X that improves circulation and promotes growth and vitality of blood vessels (e.g. gingko biloba, arganine, etc), which are all the effects normally good for you. But if you get a cancer, then cancer will use the improved blood supplies and stronger angiogenesis to feed itself, hence it will grow faster than if you had poor circulation and suppressed angiogenesis. That is then twisted to declare "X causes cancer." In fact the cancer was caused by the genes that were deliberately bred into this type mice.
More generally, onset of cancer turns values upside down -- what was good for you when you were healthy, becomes bad for you when you get cancer, since cancer will co-opt it for its own growth. What was bad for you (poor circulation, cellular toxins and pro-oxidants, heavy metals, chemo, etc) becomes good for you, since it may affect cancerous cells more than the non-cancerous cells.
A useful analogy illustrating the nature of this reversal of values in cancer, is to consider human society as a (super-)organism, which it is in many ways. In a peacetime, roads and other transport systems are good for the social organism. But in the case of war, the good transport systems often becomes a major downside since the enemy can use those roads to advance its troops and boost supply lines. In contrast, poor transportation in peacetime is bad for the social organism (backward nations). But it is also bad for the potential enemy during war. This can be easily observed on historical examples, such as WWII, where German blitzkrieg conquered the more developed nations, such as France, Netherlands, Poland very quickly, while it got bogged down in the backwards Balkans, with lots of mountains and few roads, and never really had control of those territories (except for the major cities, which were few in numbers). Similarly, in more recent wars, the backwards, mountainous undeveloped Afghanistan (or jungles of Vietnam) is practically impossible to conquer, while the more developed Iraq was overrun in weeks.
Hence, the above style of mercenary "science" using cancer mice to "prove" alleged carcinogenicity of wholesome Vitamin C or E is analogous to mislabeling transport systems and other infrastructure as a national weakness, and advocating going back to stone age, by demonstrating how much quicker the nation can be conquered if their infrastructure is good.
It is also similar to policies which mislabel personal liberty and privacy as harmful and deadly, by showing how terrorists (or drug dealers, crazies, etc) can take advantage of those liberties and privacy to cause harm. These are all the same kind of scams as the above "study" scaring people away from the vitamins C and E. All of such scare campaigns are often promoted by the very same people from the same crony front groups/NGOs, as result of natural synergies of interests -- a need to condition and herd the sheep with common scare tactics.
I actually find these kinds of "studies" quite useful, since they help me identify what is good for me -- it is always the stuff that the sickness industry is trying to scare me away from (e.g. fat, meat, eggs, bacon, cholesterol, tobacco and other ancient medicinal/entheogenic plants, etc). Further, as a rule the greater the efforts and lengths they go to with their scare mongering about X, the better X must be for me (i.e. worst for their profits). The most useful one for my health was when it dawned on me to invert "make sure have the regular medical checkups" into "stay away from doctors or hospitals" as much as possible. Last time I saw doctors was when I traveled to the 'old country' in 1991 to visit my parents, both medical doctors. In the meantime, I was mostly doing exactly the opposite from the advice of sickness industry.