News from the Annual Meeting of the American Association for Cancer Research (AACR) 2015 held in Philadelphia April 18 – 22, 2015 at the Pennsylvania Convention Center, Philadelphia, Pennsylvania
http://www.aacr.org/Meetings/Page/MeetingDetail.aspx?EventItemID=25
Disclaimer: Due to the many posters and program items covered at this meeting and to my personal inability to attend them all I will only list highlights that are of personal interest to me.
How can cancer be prevented?
Reducing tobacco use, improving diet and physical activity, reducing obesity, and expanding the use of established screening methods is recommended to avoid suffering and death from cancer.
Furthermore, vaccination against human papillomavirus and hepatitis B virus together with minimizing extensive exposure to ultraviolet radiation is recommended to reduce major risk factors of cancer.
More and more evidence has accumulated in recent years indicating that the food a human eats affects her or his risk for developing cancer. Many scientists now estimate that between 30 to 60% of all cancers are caused by environmental factors. Since all of us have to eat the type of food we eat and what lifestyle we have may increase or decrease our risk of developing cancer. In addition, there are many indications that the majority of cancers may be preventable. Altering one’s lifestyle may achieve this goal. However, the range in percentage of these estimates varies depending on which review articles are consulted.
Two out of three humans are resistant to the development of cancer and never get it.
According to George Klein two out of three humans, never get cancer. Klein suggests that resistance genes act at the level of tissue organization in a fashion that this prevents the development of cancer in close to 60% of all humans. Many genetic and epigenetic changes appear to promote cancer development and progression. But there is epidemiological evidence that a certain proportion of the human population is very resistant to the development of cancer. However, there is also further evidence that another significant proportion is highly susceptible to cancer.
George Klein has identified five to possibly six mechanisms that have anticancer surveillance functions in mammals including humans.George Klein has identified five to possibly six mechanisms that have anticancer surveillance functions in mammals including humans.
Mechanisms of cancer resistance
| Mechanism | Name | Description |
| 1 | Immunological resistance | This mechanism is acting mainly against virus-induced or virus-associated cancer. |
| 2 | Genetic resistance | A large genetic set of DNA repair mechanisms appear to be present in the human genome. |
| 3 | Epigenetic resistance | The stringency of genetic imprinting appears to contribute to this type of resistance. |
| 4 | Intracellular resistance | The optimal triggering of apoptosis in cells with incorrectly activated oncogenes or extensive DNA damage may prevent the development of cancer |
| 5 | Intercellular resistance | This mechanism is also described as micro-environmental control. It is known that normal cells can inhibit the growth of neighboring polyoma-transformed cells. Oncogens, for example, myc, ras, scr and other genetic factors may be involved. |
| 6 | HAMLET | (a newly discovered possible surveillance mechanism): This is a protein-lipid complex formed by the interaction between compounds in human milk and a lipid cofactor at the pH in the stomach of breast-fed children. HAMLET induces p53-independent apoptosis in tumor cells. However, it leaves normally differentiated cell unaffected. |
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However, it may be too early to tell how exactly these mechanisms work in detail since most disease research including cancer research study non-functioning cell mechanisms. As George Klein points out, the genetics of cancer resistance has remained largely unexplored. However, it may well be that optimal food intake and lifestyle may help normalization these surveillance mechanisms in susceptible humans and thereby help to prevent cancer in these individuals. Furthermore, it seems natural to reason that foods that contain pesticides, insecticides, fungicides or antibiotics should be avoided when selecting a healthy lifestyle.
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Genes that are involved in the development of cancer
| Genes | Function |
| Oncogenes | The normal function of these genes is the regulation of cell division. Mutations in these genes can start and support aberrant growth. |
| Tumor suppressor genes | These genes can suppress or block the development of cancer in mammals and humans. The stop the unwanted proliferation of cancer cells. Tumor suppressor genes regulate proteins that regulate cell division. A tumor suppressor gene no longer does its job when mutated. The result is uncontrolled cell growth which may contribute to the development of cancer. |
| DNA replication and repair genes | For a cell to function normally DNA replication and repair must be accurate during its life time. Any chemical change in the DNA must be corrected to keep the encoded information uncorrupted. Mutations in these genes can lead to DNA processing and repair disorders which can ultimately lead to cancer. |
| Apoptosis genes | Apoptosis or “programmed cell death” is essential for normal development of a mammalian organism. Apoptosis is a genetically regulated process of cell self-destruction. It is a normal physiological process by which DNA-damaged or unwanted cells are removed. A functional apoptotic mechanism appears to help prevent the development of cancer. Mutations in apoptosis genes can lead to pathogenesis in mammals and humans, and the development of cancer. |
The “American Institute for Cancer Research” (AICR) now suggests that most common cancers could be prevented if people ate a healthy diet, had at least 30 minutes of daily physical activity and maintained a healthy weight. Furthermore, to lower the risk for cancer AICR now recommends eating a mostly plant-based diet, limiting the intake of red meat and avoiding processed meat. Plant foods contain many kinds of substances that fight cancer such as vitamins, minerals, fiber and phytochemicals or natural occurring plant substances. Hence, organic food is the choice of food to eat since analytical studies suggest that this type of food has the lowest level of contaminations.
Phytochemicals that are present in the human diet are known to work together and help preventing cancer and other diseases.
Potentially, phytochemicals stimulate the immune system, slow down the growth of cancer cells and prevent DNA damage which may lead to cancer. However, no single phytochemical or food protects from cancer or any other disease. Therefore, eating a varied diet with lots of fruits, vegetables, beans and whole grains is highly recommended. Existing evidence indicates that this can offer the most protection against cancer and other diseases. For good health the United States Department of Agriculture (USDA) recommends to eat a healthy diet that includes fruits, vegetables, whole grains and legumes. The reported best health protection is gained when eating a wide variety of foods within each food group.
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Phytochemicals in the diet
| Phytochemicals | Plant Sources | Possible Benefits |
| Allium Compounds Allicin | Chives, garlic, leeks, onions, scallions, shallots | Slow or stop the growth of tumors. Foods in the allium family probably protect against stomach cancer. Hint: Cutting or crushing garlic at least 10 minutes before cooking makes more cancer fighters available. |
| Carotenoids Alpha-carotene | Red, orange, yellow and some dark green Fruits:Apricots, cantaloupe, citrus fruits, nectarines, papayas, peaches, watermelon Vegetables: Bok choy, broccoli, carrots, corn, greens (collards, kale, lettuce, spinach), pumpkin, red peppers, sweet potatoes, tomatoes and tomato products, winter squash | Act as an antioxidant Inhibit cancer cell growth Improve immune response Foods containing carotenoids probably protect against cancers of the mouth, pharynx and larynx.Carotenoids in dark leafy vegetables may inhibit the growth of cancers of the skin, lung, stomach and some types of breast cancer cells. |
| Flavonoids (a group of Polyphenols) Anthocyanidins (cyanidin, delphinidin, malvidin, pelargonidin, peonidin) | Fruits: Apples, berries, cherries, citrus fruits, cranberries, currants, grapes, pears, plums Vegetables: Beets, bell peppers, broccoli, celery, chard, eggplant, kale, lettuce, onions, radishes, red cabbage Beans: Black beans, kidney beans, pinto beans. Herbs: Parsley, rosemary, thyme Other: Cocoa powder, dark chocolate, coffee, tea | Support antioxidant defenses Increase the enzymes that protect the body from cancer-causing compounds Stimulate self-destruction of abnormal cells Inhibit inflammation that supports cancer growth Inhibit tumor growth Boost immune function In laboratory studies, the phytochemicals in apples reduced the growth of lung cancer cells. |
| Indoles Indole-3-carbinol | Cruciferous Vegetables: Broccoli, Brussels sprouts, cabbage, cauliflower, horseradish, mustard greens, turnips, watercress | Support antioxidant defenses Increase the activity of enzymes that protect the body from cancer-causing compounds Helps repair damaged DNA Cause cancer cells to die Decrease estrogen’s power to promote certain cancers Laboratory studies suggest that compounds found in cruciferous vegetables protect against some types of cancer. |
| Inositol Phytic acid (also called inositol hexaphosphate or IP’6) | Whole Grains: Bran from corn, oats, rice, rye and wheat Nuts Legumes: Soybeans and dried beans, | Supports antioxidant defensesSlows growth of tumors Causes cancer cells to die Laboratory studies suggest that phytic acid may prevent the formation of tumors. |
| Isoflavones (a category of flavonoids) Daidzein Genistein Glycitein | Soy: Soybeans and soy products (such as edamame, soymilk, tofu) | Support antioxidant defenses Decrease production of some hormones Inhibit growth of tumors |
| Isothiocyanates Allyl isothiocyanate | Cruciferous Vegetables: Arugula, bok choy, | Support antioxidant defenses Block tumor growth Cause cancer cells to die Inhibit inflammation that supports cancer growth Increase the activity of enzymes that protect the body from cancer-causing compounds Laboratory studies suggest that compounds in cruciferous vegetables protect against some types of cancer. Isothiocyanates form when glucosinolates in cruciferous vegetables are broken down by an enzyme released when the vegetable is chewed or chopped. |
| Polyphenols (other than Flavonoids Coumarin | Fruits: Apples. blackberries, black raspberries,blueberries, cherries, red grapes, pears, pomegranates, strawberries Other: Chestnuts, lentils, peanuts, pecans, turmeric, | Support antioxidant defensesInhibit inflammation that supports cancer growth Prevent cancer formation Cause abnormal cells to die before they can become cancerous Cell culture and animal studies suggest pterostilbene may help prevent cancer by inhibiting growth and stimulating destruction of abnormal cells.In laboratory and animal studies, resveratrol has inhibited the formation or slowed the growth of cancer.In lab studies, ellagic acid has inhibited the development of some types of cancer.In the lab, curcumin has reduced the formation and growth of cancer cells. |
| Protease Inhibitors | Legumes: Beans, lentils, peas, soybeans and whole | Inhibit cancer cell growth Prevent tumors from releasing compounds that can destroy nearby healthy cells |
| Sterols Beta-sitosterol | Vegetables: Asparagus, beets, Brussels sprouts Flax, pumpkin, sesame and sunflower seeds | Cause the death of cancer cells Lessen the inflammation that supports cancer growth |
| Terpenes (a group of Polyphenols) Carnosol | Fruits: Apples, cherries, citrus fruits, pears, prunes Bay leaves, dill, oregano, parsley, rosemary, Pumpkin seeds | Support antioxidant defenses Slow cancer cell growth Boost immune function Inhibit inflammation that supports cancer growthLaboratory studies suggest carnosol may decrease cells’ sensitivity to reproductive hormones that may promote cancer. |
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Many phytochemicals are antioxidants. These are compounds that protect the body’s cells from oxidative damage. Oxidative damage or stress is caused by an increased production of reactive oxygen species in human cells. Free radicals and other oxygen-derived species are constantly produced in the human body. Furthermore, humans are constantly exposed to oxidizing air pollutants such as ozone, oxides of nitrogen, tobacco smoke, and motor vehicle exhaust. Research has shown that a variety of antioxidant defenses have evolved in mammals including humans that protect against these reactive oxygen species. These defenses include enzymes, vitamins, and other natural antioxidants. However, these defenses are not always efficient. Many studies now suggest that antioxidants substances such as phytochemicals and vitamins found in fruits and vegetables can help the body protect against this type of damage.
References
American Institute for Cancer Research: www.aicr.org/foods-that-fight-cancer
Robert A Jacob and Betty J Burn; Oxidative damage and defens. Am J Clin Nutr 1996; 63:985S-90S.
George Klein; Toward a genetics of cancer resistance. PNAS 2009, vol. 106 no. 3, 859-863.