Cancer Prevention contains a double meaning, one is to prevent cancer and the other is to prevent cancer recurrence.
As previously mentioned, cancer development is a process. It starts from cell mutation which leads to dysplasia and then finally carcinoma in situ; this often takes several years to decades. During the process, we can take intervening measures to prevent cancer (Figure 30). The ‘Gold standard’ of cancer prevention would be to block the cancer development process before the precancerous lesion formation. Cancer prevention includes the following steps: (1) gene mutation (DNA sequence variation) and gene function changes (epigenetic changes) phase, changes in this phase often last a lifetime. In most cases, these changes may be cleared by innate or adaptive immunity; (2) from precancerous lesions to carcinoma in situ; cancer screening can help in a timely method eliminate lesions, which is mainly used for the high-risk cancer group. Appropriate intervention drugs can also be given; (3) carcinoma in situ has formed but not invaded other parts of body, drugs, surgery, nutrition or radiation therapy are mainly used to eliminate lesions to prevent dominant cancer.
For those cancer patients who have achieved effective responses to cancer treatments, the most important factor is to then prevent cancer recurrence and prolong lifespan. Like the cancer patients whom sing the song ‘No One Less’. Metastasis is the main manifestation of relapse. Cancer metastasis prevention is the same as cancer prevention and this relates directly to whether the patient can survive.
More and more experts agree with this point of view. It is impossible to kill all cancer cells for two reasons: (1) Cancer metastasis is an early event, cancer cells may exist in the blood and bone marrow even though they are at an early stage. They are in a dormancy state, once they are awoken in the future, the metastasis happens; (2) There are two types of cancer cells, one is the common type of cancer cell, the other is the cancer stem cell. So far chemotherapy and radiotherapy are noneffective towards cancer stem cells (Figure 31). So the cancer stem cells become the seeds of cancer recurrence.
The strategy of preventing cancer recurrence is to turn cancer into a chronic disease, similar to hypertension and diabetes. Long-term control could make cancer cells stay in a dormant state as long as possible, and peacefully coexist with the human body. For this purpose, it is essential to eliminate or reduce environmental carcinogens as far as possible, which has already been illustrated in the previous chapter of environmental carcinogens. I would like to mainly emphasise the following three points:
Firstly, the elimination of chronic inflammation. If cancer is likened to fire, then inflammation is the oil that keeps the fire burning.
In the 1980s, it was proved that inflammation can initiate and promote cancer growth. Rheumatoid arthritis patients have an increased risk of lymphoma and lung cancer. The longer the patient had arthritis, the greater likelihood of dying from cancer. Patients with chronic bone infection (osteomyelitis) and pressure ulcers have a tendency to suffer from progressive cancer or sarcoma; as do patients with chronic colitis. About one in every 10 patients with ulcerative colitis would ultimately have colon cancer. It is estimated that at least one-third of cancer patients once had chronic inflammation.
Conversely, inflammation control can reduce the risk of cancer progression. Three medical researches have shown that those women who had long-term use of non steroidal steroids (NSAIDs) such as aspirin or ibuprofen have significantly lower incidence of breast cancer than those women who have not taken these drugs. In a follow-up report of eight thousand women in ten years, the chance of suffering from breast cancer decreased by 23% for those women who take aspirin at least three times per week, while the risk of suffering from breast cancer reduced by 50% for those women who take Ibuprofen 2 times a week or more. One study in 1999 showed that the tumor size was smaller and the number of positive lymph nodes was less of those female breast cancer patients who had a history of long-term NSAIDs use than those whom did not take these drugs. In 2007, a study found that the chance of dying from breast cancer reduced by 36% for those patients taking NSAIDs compared to those patients not taking these drugs.
How can inflammation promote cancer progression? There are a number of mechanisms, including inflammatory cytokines which can promote the growth of cancer cells; promoting angiogenesis that provide nutrients and oxygen for cancer cells; increasing vascular permeability thereby assisting cancer cells traveling into the blood vessels and spreading to distant sites (metastasis). (Figure 32).
Secondly, the elimination of free radicals. The free radical can be likened to the wind that fans the ‘cancer fire’.
What is a free radical? It is the product of chemical oxidation. Oxidation refers to the loss of electrons from atoms or molecules. Iron rusts, apple slices brown and skin wrinkles, all of which belong to the oxidation process. The oxidation of the human body is not exactly like iron rusting, as oxygen is not necessarily involved, but oxidation can damage the body’s biological molecules. This kind of damage is caused by freer adicals.
In the process of oxidation, the atoms and molecules that lose electrons become highly-active free radicals. Oxygen we inhale and food we eat will produce free radicals in the process of oxidation. Cancer cells can also produce massive free radicals with a production rate that is much higher than normal cells. The immune cells which have been invaded in the tumor can also produce free radicals; the reason why chemotherapeutic drugs can destroy cancer cells is by free radicals produced by the drugs themselves (Figure 33).
In order to regain electrons, free radicals combine with other molecules. Any molecules including DNA may become objects combined with free radicals, resulting in cell damage. The body has an antioxidant capacity that can repair the damage in normal circumstances which will not cause harm to humans. The combination of free radicals and DNA may cause DNA mutation. If there are massive DNA mutations that fail to be repaired, this can cause cancer or exacerbate the current condition. Research indicates that free radicals can inhibit the growth of cancer genes, in other words, free radicals inhibit genes to be activated and at the same time activate genes(oncogenes) promoting cancer growth. Free radicals can also promote tumors to release cancer cells that damage vascular endothelial cells, allowing cancer cells to easily access the blood stream, which promotes metastasis.
In 2002, there was a study on three hundred and sixty-three cases of breast cancer which found that the recurrence rate of patients with significantly elevated oxidising fat molecules (free radicals) in the blood was two times higher than patients with low level of oxidising fat molecules in the blood. In 1996, it had been reported that the level of DNA damage by free radicals in patients with metastatic breast cancer was two times as high as patients with localized breast cancer.
Thirdly, the maintenance of immune function. As mentioned above, immune function can regulate and maintain the balance of cancer cells. The immune function can be likened to a wall, to prevent the spread of cancer cells or at least to maintain a peaceful coexistence with cancer cells.
In order to eliminate chronic inflammation, free radicals and maintain immune function, we should maintain a good lifestyle and get rid of certain lifestyle habits that can promote free radicals and inflammation formation.
I give lectures around the world. Many people, especially cancer patients always ask me how to prevent cancer recurrence? I tell them gaining ‘balance’ is most important. Human beings originated one million years ago and the bulk of human DNA reflects that historic environment. Cancer was once considered a cynically rare disease historically whereas now cancer threatens almost every family. This is due to the rapid development of society and environmental changes, to which the DNA of human beings has had no time to adapt, resulting in cell mutation and cancerous changes.
‘Balance’ includes a balanced diet, static and dynamic balance, balanced mentality and immune balance. To maintain homeostasis in the most natural way seems to be the basic strategy of cancer prevention and cancer recurrence prevention.