This article is not meant to be an exhaustive discussion of cancer preventive supplements. As well, there is no guarantee that supplementing various vitamins and minerals will absolutely prevent cancer in any one individual. I definitely think that supplementation of the following hormones, vitamins, and minerals will lower the rate of cancer in the population. It is your choice to either follow my counsel or not.
Remember one simple fact: death is not a tragedy, it is an absolute certainty. Your goal should be to live a long and healthy life. It is with that in mind that I write these recommendations.
There are a number of things to do to prevent cancer:
Avoid and rid of environmental toxins [1, 2]
Exercise [3, 4]
Cancer preventive hormones
Vitamins, minerals, & herbs known to prevent cancer
I have already outlined the hormones that have proven cancer preventive effect:
D3 or Cholecalciferol [5, 6]
Melatonin [7, 8]
Progesterone [9, 10]
DHEA [11, 12]
But, in this article, I want to discuss those non-hormonal substances that have cancer preventive effects.
Many substances have been shown to have a protective effect against cancer. Conservative advocate of nutraceuticals, Ray Sahelian, MD, lists a number of them . Dr. RH Liu of Cornell University, describes the synergy obtained from taking a number of them concurrently .
With all of that in mind, I advise using the following expressly listed 4 supplements:
Iodine causes fluid to move more rapidly through tissue. Perhaps this effect is one way for prevention of stasis or clogging of milk ducts and prostate tissue with secretions made less fluid by the absorption of liquid components. How about the word, gunk? Or, maybe, sludge. So, these inspissated secretions, or gunk, which failing to be removed, are thought to be the source points of cancer degradation. Iodine prevents their formation. Another result of iodine deficiency in glands is the formation of cysts & nodules, you know, like breast cysts, thyroid nodules, and ovarian cysts. Iodine is required for the formation of the correct architecture of glands .
Iodine's powerful anti-cancer activity lies in its control of apoptosis, or programmed cell death, centering on killing cancer cells . Selenium works synergistically with iodine .
Products of iodine containing a mixture of elemental iodine and potassium iodide in doses of 6¼ to 12½ mg consistently taken daily along with 100 to 200 mcg of selenium provide apoptosis of cancer cells . Some patients take as much as 25 to 50 mg of combination iodine & iodide product without side effects, consistently, daily, describing feeling more energetic. Such patients did so not by my recommendation, but on their on.
Regardless of how it works, iodine has been proven to have a preventive effect against cancer of the stomach, breast , lung, liver, colon and prostate. And it likely has a general anti-cancer effect  .
Bromine and fluoride, other halogens, displace iodine, causing an iodine deficiency. Bromine has been added to flour as an anti-caking agent and fluoride, implicated in lowering IQ’s of children, is in so much of our drinking water. Both displace iodine. Both block iodine from getting to the breasts where it is essential .
There is no allergy to molecular iodine nor to potassium iodide. Every human possesses iodine. In order for an allergic reaction to occur, a molecule must be large enough to elicit an allergic response. Such reactions to large iodine containing molecules are commonly seen after ingesting sea food or after being administered iodine containing radiographic dyes.
There has been sound scientific evidence that vitamin C prevents cancer for 25 years . It is well known that high dose vitamin C given intravenously selectively kills cancer cells [22, 23]. “It has been greater than 50 years since it was first hypothesized that ascorbate may inhibit tumor growth.”  So, you can see that the comprehension of this effect is nothing new. You may consider this effect a preventive measure when just tiny numbers of cancer cells have formed very early in the carcinogenic process.
Vitamin C cannot be produced in humans, a very unfortunate state of affairs for us. Rodents can produce huge amounts of vitamin C when under stress, allowing them to recover faster.
For cancer prevention, how much Vitamin C should you take? The tolerated dose varies from person to person, with the maximum dose swallowed bordered by “bowel tolerance”, or the dose at which diarrhea begins. And, for many people, that dose is 3,000 mg per day. I think that 2,000 mg per day for most people produces a preventive effect.
Curcumin is an extract of Turmeric . The spice is widely used in Asian cuisine.
“The incidence of cancer is significantly lower in regions where turmeric is heavily consumed.” For that matter, so is the incidence of Alzheimers . Curcumin reduces inflammation and neurodegeneration [27, 28]. To me, that’s a good enough reason to consume it. But the evidence that the spice prevents cancer is overwhelming. “Numerous studies have demonstrated that curcumin possesses antioxidant, anti-inflammatory, and anticancerous properties.” Studies show benefit of taking curcumin regarding colorectal cancer , lung cancer , prostate cancer , breast cancer , and cancer of the pancreas .
So, how much should you take? Basically, it’s not known . Further, Curcumin is not very soluble in water, and absorption from the gut is low. However, absorption can be increased with the addition of bioperine , a black pepper. In my opinion, for cancer prevention, you should take 900 mg or more of Turmeric extract or curcumin with bioperine.
Trans-Resveratrols are found in grapes, peanuts, and cranberries & other berries. They are known to prevent cancer generally, but especially colorectal cancers by 3 specific pathways . “These data suggest that resveratrol.... merits investigation as a potential cancer chemopreventive agent in humans.” “Besides cardioprotective effects, resveratrol exhibits anti-cancer properties, as suggested by its ability to suppress proliferation of a wide variety of tumor cells, including lymphoid and myeloid cancers; multiple myeloma; cancers of the breast, prostate, stomach, colon, pancreas, and thyroid; melanoma; head and neck squamous cell carcinoma; ovarian carcinoma; and cervical carcinoma.” 
The current variety of opinion is regarding the avenue to obtain the best cancer preventive effect.
Should we seek cancer prevention from diet alone? Or if we supplement trans-resveratrol, what is the best dose?  Moreover, it has come to light that there may well be a “biphasic” response to various doses of resveratrol, where benefit is seen with a small dose, and lost when larger doses are used .
Supplement guru, Ray Sahelian, MD, favors a low dose, stating that he takes 10 mg once or twice weekly [42, 43]. Yet, he sells 40 mg and 50 mg capsules as well. Other marketers commonly sell 500 mg capsules . Side effect have been described , but have not been clinically obvious to practitioners. Still, with large doses, in the range of thousands of milligrams, changes in the absorption and metabolism of drugs and metals have been measured and are worrisome . At this point in time, I suggest sticking to doses of 500 mg or less per day.
There is a lot of information in the medical scientific literature that has not been translated into patient advocacy by medical professionals. Hopefully, this information and the following bibliography will whet your appetite for learning more about cancer prevention.