There have been many studies done to see if fiber in food can have an anticancer effect in the human body. There is little doubt that the western diet and lifestyle increase the risk of many cancers since societies such as those seen in rural Africa have very low incidences of many cancers. This study reviewed 9 studies done in humans and not animals. 2 of the studies tested oligofructose-enriched inulin. Positive effects were seen with this prebiotics. However, no cancer claim can be made. Prebiotics just may put you into a different group.

Beneficial modulation of the gut microbiota

Short-chain fatty acids (SCFA) are the stars of the prebiotic story. These substances are made in copious amounts when the best colon bacteria are fed with prebiotics. One SCFA is called proportionate. It is made by the good colon bacteria and then slips into the blood and goes to the liver. There it has been found to have a remarkable effect in preventing the growth of liver cancer cells. This was a mouse study and no claims can be made for its use in humans but the research is very interesting.

Gut microbiota-derived propionate reduces cancer cell proliferation in the liver

A recent article in the prestigious journal Cell again links detrimental changes in the gut microbiome to inflammation and then to cancer.
While a cause and effect still remain to be determined, the link between dysbiosis of the gut and colon cancer is now stronger than ever.

A recent publication from Garcia-Peris et al. (EJCN 2015) shows data that indicates that oligofructose-enriched inulin may provide benefits for patients undergoing radiotherapy, in this case by improving the consistency of stools.