Chemoprevention of bladder cancer.
Kamat AM; Lamm DL
Urol Clin North Am 2002 Feb;29(1):157-68
Prospective randomized trials with a large sample size, long follow-up, and an extended duration of treatment are needed to clarify the association between micronutrients and cancer protection. With these caveats in mind, several recommendations can be made. Simple measures, such as drinking more fluids (especially water), can have a profound impact on the incidence of bladder cancer. Vitamins are being extensively studied in chemopreventive trials for different cancers. There is strong evidence for a chemoprotective effect of vitamin A in bladder cancer. The authors recommend 32,000 IU/day of vitamin A initially, with lower doses (24,000 IU) for persons less than 50 kg. Because liver toxicity is a possibility with long-term administration, the dose should be decreased to 16,000 IU after 3 years. High doses of beta-carotene should be avoided based on a large clinical trial reporting a 25% increase in the number of cases of prostate cancer and a statistically significant increase in the incidence of lung cancer. Vitamin B6 has been studied in several clinical trials in bladder cancer. The US-based Veterans Administration cooperative study found benefit for vitamin B6 when given as a single agent. Data for vitamins C and E are insufficient to recommend either agent as stand-alone treatment. Nonetheless, each of these vitamins is known to have beneficial effects, including improved function of the immune system. It is possible that only a small percentage of patients with bladder cancer respond to vitamins B6, C, or E, yet each is safe, nontoxic, and inexpensive. In an effort to pool the efficacy of individual agents and to increase the power of study, the authors evaluated the combination of vitamins A, B6, C, and E in a double-blind trial. The observed 50% 5-year reduction in tumor recurrence was highly significant and greater than would be expected for any of the individual ingredients and suggests that combinations of nutritional agents may be most appropriate. A large-volume study along similar lines is being conducted. Among the numerous other compounds and dietary substances purported to have chemopreventive effect, soybeans, garlic, and green tea stand out as having the greatest promise and can freely be recommended to patients. For synthetically synthesized agents such as celecoxib, piroxicam, or DFMO, recommendations must be deferred until the results of clinical trials are conclusively in favor of their use. Many of the dietary factors found to be protective against bladder cancer are being investigated in other cancers and are beneficial to general health. Although naturally occurring nutrients are ideal, especially because the delicate balance of various micronutrients might be impossible to synthesize in the laboratory, the general population finds it easier to take vitamin supplements. Unfortunately, dietary changes such as decreasing fat and increasing fruit and vegetable intake are more difficult to initiate. There is a mistaken notion that simply because an agent is naturally occurring, it cannot be as beneficial as taking a substance synthesized in the laboratory. Even in a high-risk group such as nuclear-bomb survivors in Japan, high consumption of vegetables and fruit is protective against bladder cancer . Encouraging patients to follow an essentially healthy food habit lifestyle will be a significant contribution in the fight against cancer.