That is a big unknown because it has never been studied by the medical community,...(you cant do a double blind placebo controlled study on enemas,, you either got an enema or not) it may be possible to interview patients to see if they have done enemas and use the data to develop a profile....
it is well known that waste that remains in the colon too long can rot and does produce cancer causing toxins including: indole, scatole and a host of others! it is even possible that the types and ratio of colon bacteria can contribute to colon disease..one example is this new super bug called "c. diff" it got to super bug status by using anti-biotics which killed off normal colon bacteria and allowed the resistant c. diff to survive!
and i think it would depend on frequency and exactly what you are using for enema solutions,,,i.e.: pure water, coffee, green tea, wheat grass all could be candidates for study,,
alternatively.. substances that could actually increase cancer risk might include: soaps, alcohol, vaseline, mineral oil, etc....and has anyone read the warning label on those nasty fleet type enemas! (another product developed in the name of greed)
it is also well understood that corporations seem to have discarded common sense and will put most anything in our food in the name of profit, so we are constantly bombarded by a steady supply of toxins, all of which can contribute to the problem..remember when they told us that butter was bad and hydrogenated oils was good!!
I am NOT A DOCTOR, i have partied with some,, and i have studied everything i could find on enemas for many years..so for me i prefer to get the waste out of me in a timely basis, that means a daily enema with pure water and/or organic coffee, organic olive oil for lube. eliminate hydrogenated oils from my diet, ...
I have read reports of people who claim to have cured their own cancer with diet and wheat grass enemas,, and the gerson clinics use coffee enemas in their cancer treatment centers...