Coffee is a complex mixture of compounds and there is evidence that drinking certain types of coffee is associated with a reduction in incidence of some cancers, including prostate cancers. By studying the effects of two compounds found in coffee, kahweol acetate and cafestol, on prostate cancer cells and in animals, they were able to inhibit growth in cells which are resistant to common anti-cancer drugs such as Cabazitaxel.
The researchers initially tested six compounds on human prostate cancers cells in vitro (i.e. in a petri-dish). They found that cells treated with kahweol acetate and cafestol grew more slowly than controls. They then tested these compounds on prostate cancer cells which had been transplanted to mice (16 mice). 4 mice were controls, 4 were treated with kahweol acetate, 4 with cafestol, with the remaining mice being treated with a combination of kahweol acetate and cafestol.
The combination worked best. After 11 days, the untreated tumors had grown by around 3 and a half times the original volume (342%), whereas the tumors in the mice treated with both compounds had grown by around just over one and a half (167%) times the original size.
The scholars were careful to note that this is a pilot study in mice. If you read bombastic claims from mice studies showing a chemical is killing you or a miracle vegetable is making you live longer, it should be denied on that basis alone. Mice studies can never show a link, they can only eliminate one. If a link is found, it then goes to human studies so mouse studies are always exploratory.
So no matter what Dr. Oz or someone on The Doctors claims, don't double your coffee consumption or eliminate any food based on a mouse study