Cancer is a scary thing to hear. In fact, there are indeed few cases of cancer patients around the world. in February 2015, the American Chemical Abstracts (CA) published online “Global Cancer Statistics 2012”: in 2012, there were about 14.1 million new cancer cases and 8.2 million patients died of cancer worldwide; 57% of cancer patients and 65% of cancer deaths came from developing countries. Lung, liver, colon and prostate cancers are the big enemies of men, while female cancer cases are more frequent in lung, breast, colon and cervical cancers. China, as the world’s largest developing country, cancer is the biggest hidden threat to the nation’s health and a matter of great concern to the government. As early as 2012, when the news of a family of three suffering from lung cancer in Shenyang was reported, people were worried that “is cancer contagious?” In the past six months, there have been rumors that “data from famous foreign journals show that cancer may be contagious”, which triggered waves of online discussions. In fact, cancer is not contagious, and the so-called “data from famous foreign journals” is suspected of deliberately exaggerating and misinterpreting the results of published experiments abroad. Two “superpowers” of cancer cells Why is cancer so difficult to be cured? The normal cells of our body follow the law of “grow-differentiate and die”. For a healthy adult, newly generated cells will replace the dead cells and the number of cells is basically constant. In the case of cancer cells, the “grow-differentiate die” rule does not apply, and it has two superpowers. The first superpower: it is completely out of the control of the organism and can proliferate freely and indefinitely, becoming a myth of “immortality”. The second superpower: it is no longer bound to the local tissues like normal cells, and the liberated cancer cells can metastasize and infiltrate other tissues like a “nest”. Cancer cells are mainly transferred through blood vessels and lymphatic vessels, through which they can spread throughout the body, which makes cancer uncontrollable. Some people think that cancer patients have an extra oncogene in their bodies, but in fact, we all have proto-oncogenes in our bodies. However, the existence of proto-oncogene does not mean that we have cancer cells in our body. The proto-oncogene is responsible for cell division and proliferation, and is needed for normal growth of the body. At the same time, in order to control the proto-oncogene, there are also oncogenes in the body. The proto-oncogene and the oncogene control each other and maintain the balance. However, under the action of oncogenic factors, the balance between them is broken and cancer cells are induced. Therefore, oncogenic factors are the key to unlock cancer cells, which include mental factors, genetic factors, lifestyle, certain chemical substances, etc. Cancer cannot be transmitted, what can be transmitted is the virus or bacteria related to cancer Although cancer is very powerful, the worry of being infected with cancer is a bit unfounded. It is certain that cancer patients cannot transmit cancer cells to healthy individuals. To date, there is no international scientific evidence that directly proves that cancer can be transmitted through kissing, touching, sex, sharing utensils, and other daily lifestyle activities. Our body’s immune system is so sophisticated that it can recognize the body’s own cells and attack and remove all foreign invading viruses, bacteria, etc. Of course there have been cases where cancer cells can be transferred from the donor’s organ to the recipient through organ transplantation. This is not a case where cancer cells can be transmitted, but rather individuals who receive organ transplants are heavily medicated with immunosuppressive related drugs after the surgery, weakening the immune system’s ability to respond, thus making the body unable to effectively destroy and remove cancer cells without rejecting the transplanted organ. For a healthy person, even if he is exposed to a certain number of cancer cells, he will be fine because his immune system will quickly remove all the cancer cells he comes into contact with, which is a unique advantage that human beings have gained by evolving to the top of the pyramid. Many cancers are associated with viral or bacterial infections. Cervical cancer is associated with human papillomavirus infection, nasopharyngeal cancer with EBV, liver cancer with hepatitis B virus, and stomach cancer with Helicobacter pylori. These viruses and bacteria can be transmitted during everyday person-to-person contact, but it is not a given that individuals infected with these viruses or bacteria will get the associated cancer. For example, H. pylori infection can lead to gastritis, while gastric cancer requires a series of processes such as “H. pylori infection – chronic superficial gastritis – chronic atrophic gastritis – heterogeneous hyperplasia – gastric cancer”, etc. With early prevention and treatment, gastritis can be completely prevented from developing into gastric cancer. Therefore, the fact that virus and bacteria can be transmitted does not mean that cancer can be transmitted. Stomach cancer five-part series Track the rumors and seek the truth Rumor 1: In November 2014, according to a paper published in Cancer Cell, “breast cancer exosomes” can cause normal cells to become tumor cells, and normal cells transformed by “exosomes” can produce tumor cells in mice. The normal cells transformed by exosomes can produce tumors in mice. Cancer can be transmitted by exosomes. Exosomes, 50-140 nm vesicles, contain proteins and nucleic acids that act as “beacons” to influence the physiological activities of neighboring cells. In the article, the authors injected normal cells that had been affected by exosomal “beacons” in vitro into nude mice, which developed tumors. But what is a nude mouse? The nude mouse does not have a thymus, an important immune organ, and lacks T cells, which are essential for the immune response, and its immune system is incomplete. As mentioned before, for individuals with a normal immune system, even if they are exposed to a certain number of cancer cells, they will be fine. Therefore, the nude mouse model does not prove that cancer can be transmitted in healthy individuals. In addition, most of the experiments in the article are in vitro experiments and are still a long way from clinical trials. Rumor 2: In April 2015, the internationally renowned journal Cell published a paper claiming that when blood cells from soft-shell clams with leukemia were injected into healthy soft-shell clams, some of them would unfortunately get hit and develop leukemia. Cancer can be contagious. Humans, being vertebrates, have an immune system that can selectively attack foreign invading bacteria and viruses while ensuring that it does not attack its own normal cells. This ability to selectively attack is due to the “threshold” set during the development of the human immune system: all immune cells that can attack their own cells are killed in the “cradle”. Soft-shell clams, invertebrates of the mollusk family, are at the bottom of the evolutionary pyramid compared to humans, without the “threshold” used for censoring or with a different “threshold” for censoring, and their immune system is completely incomparable to that of humans. Therefore, the model of molluscum contagiosum also cannot prove that cancer is contagious in the population. Rumor 3: A family of three in Shenyang all got lung cancer, and cancer cells are contagious as they appear in family-like clusters. Factors that can induce cancer, called carcinogenic factors, include mental factors, genetic factors, lifestyle, certain chemical substances, etc. The family-like clustering of cancer is related to the family having the same living habits and being in the same living environment. In a family of three in Shenyang, the husband is a smoker and the wife and children are in the environment of second-hand smoke for a long time, and we know that nicotine in smoke is the main culprit of lung cancer. Therefore, the lung cancer of the wife and children is more likely to be induced by nicotine in secondhand smoke than by the husband’s lung cancer. Moreover, cancer appears to be aggregated in this family, but this is an extremely rare and isolated phenomenon, and there are no global or national statistics of large samples to prove the phenomenon of family-like aggregation of cancer. Cancer, cannot be transmitted.