Many people in the breast surgery team of Zhongshan Second Hospital have developed cancer. Is it really the reagents that are to blame?

The hospital responded quickly to the online rumor that "many members of the breast surgery research team of Zhongshan Second Hospital have cancer." However, for the general public, the credibility of the "rumor-busting" may not be stronger than the rumor. In this case, logical thinking combined with scientific common sense is still our basic means of distinguishing right from wrong.

Written by | Wang Chenguang

On November 7, there were rumors in the self-media that many members of the breast surgery research team of the Second Affiliated Hospital of Sun Yat-sen University had cancer. The rumors were vague, but the intention and direction were clear, that is, the research team was doing research on tumors, and the rumors said that the cancer of many members of the research team was directly related to their laboratory work. The rumors also included that the research team used carcinogenic reagents to build tumor models in animals, and even mentioned that the head of the research team convened a meeting afterwards and asked to clean up these reagents from the laboratory as soon as possible.

The incident quickly escalated. Just a few hours later, I received WeChat inquiries from many friends from different fields about this incident, asking about the possibility of this happening. My reply was that it was impossible for the rumor to happen that so many people would develop breast cancer and pancreatic cancer in a short period of time.

The reason why I dare to make this conclusion before the relevant authorities respond is based on the speed of tumor development. The general public often does not understand this question: How long does it take for a malignant tumor to grow (to a detectable degree)?

The simple answer is: a long time. The exact length of time varies from person to person and from tumor type to tumor type. In general, tumors develop much more slowly than most people imagine, taking ten, more than ten, or even decades. This is different from what some people think. Most tumor patients are diagnosed after seeking medical examinations after symptoms appear, which can easily lead to misunderstandings that tumors occur and form shortly before symptoms appear.

To understand this problem, we need to first have a general understanding of the tumorigenesis process. There are many theories on tumorigenesis, and the most time-tested and dominant one is the "mutation selection" hypothesis. The medical science community generally believes that no matter how large or heterogeneous the tumor is, it starts from a single cell. In other words, at the cellular level, tumor development is seen as a multi-step process involving mutations and (natural) selection of genes within the cell, and its ability to survive, proliferate, invade, and metastasize is gradually enhanced.

The first step is tumor initiation, which is the occurrence of certain genetic changes in cells, which eventually lead to the ability of individual cells to proliferate indefinitely.

The initial cell continues to proliferate and become a group of cells, which is called the clonal growth of tumor cells. This group of cells continues to mutate as they proliferate. Most cells stop proliferating and eventually die after their genes mutate, but some of these mutations give cells a selection advantage, such as faster growth. The descendants of cells carrying this mutation will dominate the tumor population. This process is called clonal selection, which is also the second stage of the tumor, namely the tumor progression stage.

Clonal selection continues throughout the development of the tumor. Some clones acquire invasive capabilities and begin to invade surrounding tissues. This is the third stage of tumor development, the invasiveness stage.

Eventually, tumor cells enter the lymph and blood and then reach other tissues and organs, taking root and beginning to grow. This is the final process of tumor development, namely metastasis.

The rumor involved a pancreatic cancer patient who was less than 30 years old. As we all know, pancreatic cancer is a highly malignant cancer. Once diagnosed, patients often only have a few years or even months to survive. But among all cancers, pancreatic cancer does not develop quickly.

Pancreatic cancer is difficult to detect in its early stages because it often shows few symptoms and current imaging techniques do not have much advantage in detecting pancreatic cancer. The vast majority of pancreatic cancers are diagnosed when patients seek medical treatment when they have symptoms, which is already past the early stages of development.

Studies have found that it takes at least ten years for the first cancer-causing mutation in pancreatic diseased cells to transform into cancer cells. After the first cancer cell appears, it takes an average of nearly seven years to divide into billions of cells before it can be discovered by imaging technology. Most pancreatic cancers have already metastasized when they are discovered, and from this point on, patients die within an average of two and a half years.

The rumor also mentioned that six members of the research team had breast cancer at the same time, and none of them were under 30 years old. This is even more incredible. The development of breast cancer is also a long process (lasting for decades) . The author has decades of experience in cancer research (mainly in the direction of breast cancer), and I don’t know what kind of research reagents (including carcinogens for tumor modeling in animals) can so effectively induce tumors in humans in a short period of time (within a few years).

Here we need to briefly understand carcinogens. As the name suggests, carcinogens are any substances that can cause cancer. It is very important to identify possible carcinogens so that we can take targeted measures to avoid exposure to them. The National Toxicology Program of the U.S. Department of Health and Human Services and the International Agency for Research on Cancer of the World Health Organization have classified substances that are known or reasonably expected to be human carcinogens. To date, more than 500 substances have been classified as possible or confirmed carcinogens to humans, including asbestos, automobile exhaust, processed meat, and ultraviolet rays.

Carcinogens can be divided into the following categories according to their sources:

Chemical carcinogens include carcinogens emitted into the environment by human beings, such as automobile exhaust, industrial products and byproducts, and cigarette smoke. Carcinogens in cigarette smoke include benzopyrene, dimethylnitrosamine, and nickel compounds, which are confirmed human carcinogens. Smoking (including secondhand smoke) is the cause of more than 90% of lung cancer, and smoking is also associated with cancers of the mouth, throat, esophagus, and other parts of the body.

Environmental carcinogens include ultraviolet rays in sunlight, high-energy radiation in the environment (such as radon gas), and mycotoxins. Ultraviolet rays are the main cause of skin cancer, radon gas is the second largest cause of lung cancer after tobacco, and aflatoxin produced by food mold is an important carcinogen for digestive tract tumors.

Biological carcinogens are mainly viruses that can change the genes of human cells, such as human papillomavirus (HPV), Epstein-Barr (EB) virus and hepatitis B virus.

Regardless of the type of carcinogen and regardless of its carcinogenic mechanism, it ultimately needs to induce changes in the genes within human cells, and then go through the steps and processes of tumor occurrence and evolution mentioned above before it can finally develop into a detectable tumor.

Different carcinogens can cause different types of cancer depending on how they come into contact with human tissues and organs. Moreover, exposure to carcinogens increases a person's risk of developing certain cancers, but it does not mean that a person will definitely develop cancer. There are many factors that affect whether a person exposed to carcinogens will eventually develop cancer, including the dose and duration of exposure, exposure to other environmental factors, and a person's genetic background.

The person in charge of the research team involved in the rumor is the director of the Breast Cancer Research Center of Sun Yat-sen University, whose main research direction is immunotherapy for breast cancer. With the knowledge of the occurrence of the above cancers, we can know that the rumor that "six young scholars (students) under the age of 30 in the research team suffer from breast cancer at the same time" does not stand up to scrutiny: the currently identified carcinogens (including the carcinogens used in the research), no matter what type of cancer they can induce, are unlikely to develop into detectable malignant tumors in a short period of time; tumors induced by carcinogens are more likely to be concentrated in the digestive system, respiratory system, skin and circulatory system, which are easily in direct contact with carcinogens. Although it is not ruled out that some carcinogens will increase the risk of breast cancer, the impact will be much lower in relative terms.

To take a step back, even if there are really multiple cancer patients at the same time in a research group of dozens of people, this is an extremely low-probability event, and it is difficult to establish a direct connection with the research environment of the research group.

During the writing of this article, the author learned that Zhongshan Second Hospital responded to the rumors at around 2 a.m. on the 8th. It is foreseeable that a considerable number of the public will not believe the hospital's explanation and statement - after all, not every member of the public can clearly understand that the occurrence of cancer is a long process.

Hospital response

The author of this article is a PhD in biology. He has served as a researcher at the Sidney Kimmel Cancer Center of Thomas Jefferson University, an associate professor in the Department of Cancer Biology, and a professor at Peking Union Medical College. He is currently engaged in the research and development of anti-tumor drugs.

This article is supported by the Science Popularization China Starry Sky Project

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.

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