I believe vitamins and minerals are very important to our health, especially if we are not getting what we need from our diet.  Recently, Dr Oz had on a Naturopathic doctor that talked about 4 supplements that fight cancer. They were IP-6, Selenium, Black raspberry and Vitamin D.  There has been a lot of evidence that Vitamin D is very beneficial in fighting cancer.  I believe checking into the other 3 he mentioned could also be of benefit.  Check with your doctor before adding anything to your regimen.
And you can't beat a healthy diet and exercise - they are your best defence!