From Wikipedia:
Some proponents of alternative medicine have claimed that coffee enemas have an anti-cancer effect by "detoxifying" metabolic products of tumors. There is no medical scientific evidence to support any anti-cancer effect of coffee enemas.
Coffee enemas can cause numerous side effects, including infections, sepsis (including campylobacter sepsis), severe electrolyte imbalance, colitis, proctocolitis, salmonella, brain abscess, and heart failure. If the coffee is inserted too quickly or is too hot, it could cause internal burning[14] or rectal perforation.[15] Long term use of coffee enemas can lead to malabsorption of fat, fat-soluble vitamins, and calcium.
The use of coffee enemas has led to several deaths as a result of severe electrolyte imbalance, hyponatremia, dehydration, pleural and pericardial effusions.[8][16] The U.S. Food and Drug Administration (FDA) has ruled that study participants must be warned of the risk of death from coffee enemas in studies that use them
why would anyone want to try this is beyond me