Researchers from the Harvard and Ohio State universities found that men who eat less than a serving of broccoli a week have more than double the risk of contracting bladder cancer than those eating two or more half-cup servings a week. Isolated compounds of broccoli were found to change into isothiocyanates (sulphoraphane) when it is chopped, chewed and digested. These "nutritional powerhouses" are believed to inhibit the development of bladder cancer.

The broccoli had the most profound effect on the most aggressive form of the cancer, human invasive transitional cell carcinoma.

Young broccoli sprouts have the highest concentrations of these phytochemicals, but broccoli in any form was found to have the desired effect.

Study co-author Steven Schwartz said that their studies continue.
“We’re starting to look at which compounds in broccoli could inhibit or decrease the growth of cancerous cells,” he said. “Knowing that could help us create functional foods that benefit health beyond providing just basic nutrition.”
The researchers believe other members of the broccoli family, like cabbage, cauliflower, Brussels sprouts and kale may have the same effect on pre-cancerous cells.

Note also the following research evidence

·              Bladder cancer

"Two hundred fifty-two cases of incident bladder cancer were diagnosed from 1986 through January 31, 1996, among 47,909 men enrolled in the Health Professionals Follow-up Study. Each participant in this cohort completed a 131-item food frequency questionnaire in 1986 and subsequently in 1990 and 1994. We used logistic regression analyses to examine fruit and vegetable intake in relation to bladder cancer risk, after adjusting for age, history of cigarette smoking, current smoking status, geographic region, total fluid intake, and caloric intake. We observed a weak inverse association that was not statistically significant between total fruit and vegetable intake and bladder cancer risk. Intake of cruciferous vegetables was inversely associated with risk (relative risk = 0.49; 95% confidence interval 0.32-0.75, for the highest category of cruciferous vegetable intake compared with the lowest), but intakes of yellow or green leafy vegetables or carotenoid-rich vegetables were not associated with risk. Individual cruciferous vegetables, except for coleslaw, were all inversely related to bladder cancer risk, but only the associations for broccoli and cabbage were statistically significant."

The anti-cancer effect of brassicas and other fruit and vegetables have also been found for other cancers besides bladder cancer.