When it comes to health, prevention is better than cure. Over the last 50 years the use of statins, B-blockers and aspirin has prevented half of the deaths from heart disease. Researchers are keen to see whether something similar can be achieved for the prevention of cancer. Over the summer the BBC reported that cabbage may help prevent bowel cancer. Is it worth looking at cabbage beyond more than a trendy super-food?
What is chemoprevention?
The use of drugs, vitamins, food supplements or other agents to reduce the risk of, or delay the development or recurrence of a disease is called chemoprevention. Research looking for agents to prevent cancer began in the 1990s. At first, results were not very promising. A study hoping to reduce the lung cancer incidence of heavy smokers and asbestos-exposed workers through the use of micronutrients (beta-carotene and vitamin A) supplements was stopped early because these were found to increase the risk of lung cancer by nearly a third compared to those on placebo. A similar study of selenium and vitamin E and prostate cancer was stopped early as no benefit was found.
The biggest cancer chemoprevention success to date has been the discovery of aromatase inhibitors (Anastrazole) and selective oestrogen receptor modulators (such as Tamoxifen) for breast cancer prevention. Women at high risk of breast cancer who take these drugs for five years are a third less likely to get breast cancer over the following 10-20 years – a considerable reduction.
Food supplements as chemo-preventative agents
In the recent report of cabbage in bowel cancer, researchers used mice to explore the biological mechanisms behind the chemoprevention characteristics of cruciferous vegetables (such as kale, cabbage and broccoli). They found that a compound in called indole-3-carbinol (I3C) and its by-products which are made during acid digestion reduce gut inflammation thereby preventing colon cancer.
Our research group are no strangers to fighting cancer with cabbage. Ten years ago we carried out a clinical trial to find out whether cruciferous vegetables could help prevent cervical cancer. We used Diindolylmethane (DIM) supplements – DIM is formed from indole-3-carbinol (I3C) during digestion.
At the time, evidence suggested that DIM caused the ‘death’ of tumour cells in the cervix, breast, endometrium, ovary, prostate and colon. Furthermore, one study showed that in mice DIM helped clear Human papilloma virus (HPV) infections and altered oestrogen metabolism inhibiting cervical disease. Unfortunately, our study showed no effect of DIM on HPV clearance or on cervical abnormalities. Nevertheless, the most recent ‘cabbage’ study brings us a step closer to understanding how I3C works and taken together with previous published evidence suggests this agent is worth exploring further.
Cancer chemoprevention is a very exciting and dynamic field. However, there are also enormous challenges to overcome. Although Tamoxifen can provide impressively long term protection against breast cancer, surprisingly nearly 9 out of ten women offered the treatment refuse it. The most common side effects of Tamoxifen are more bothersome than serious: hot flushes, tiredness and nausea. It is worth mentioning that in our cabbage study the dosage used was many times that which could be obtained from eating a diet rich in cruciferous vegetables. Hence women taking the supplements experienced bloating and flatulence. So, asking those who are fit and well to endure side effects for many years is no small task.
It also seems hard to get the message out: a study found that only half of GPs surveyed in England knew that Tamoxifen can reduce breast cancer risk.
So, it seems the road ahead for cancer chemoprevention could be long and steep. But given that 1 in 2 people will be diagnosed with cancer in their lifetime, finding effective ways to prevent cancer will be just as important if not more so than finding new cures.
The views expressed are those of the author. Posting of the blog does not signify that the Cancer Prevention Group endorse those views or opinions.