The number of cancer patients in China is increasing rapidly. Well-known epidemiology experts give advice on how to “fight cancer”?

Introduction

China is the country with the highest cancer burden in the world. In order to better understand the epidemic trends of cancer and take corresponding countermeasures, we interviewed Zhang Zuofeng, director of the Department of Epidemiology at the UCLA School of Public Health and an outstanding epidemiologist.

Professor Zhang Zuofeng graduated from the School of Public Health of Shanghai Medical University in his early years. He has served as a member of the Cancer Epidemiology Project Review Expert Group of the National Institutes of Health, a senior member and director of the American College of Epidemiology.

Professor Zhang has always been concerned about the development of public health in China. He has conducted extensive research on the causes of the prevalence of different cancers. From the 1990s to the present, he has done a lot of outstanding work in the field of cancer. Today, we interviewed Professor Zhang about the prevalence trend of tumors in China.

01 Differences between cancer incidence trends in China and those in Europe and the United States

Ye Shuisong: China has a large number of cancer patients and a heavy tumor burden. The number of patients with lung cancer, breast cancer, and colorectal cancer has remained high. What do you think of the trend of cancer incidence in China? What are the differences between these cancers and the prevalence in Europe and the United States?

**Zhang Zuofeng: **In general, the incidence of cancer in the world is increasing, and the mortality rate of cancer is decreasing. However, because China has a huge population, the number of cancer cases and deaths in China ranks first in the world.

In the past 10 years or so, the main traditional tumors in China - esophageal cancer, gastric cancer, liver cancer and lung cancer - have several basic characteristics:

First, the mortality rate is high.

Second, it is related to people’s living standards.

Third, it is related to people’s living habits and even to infection.

Gastric cancer, esophageal cancer and liver cancer are all major tumors, accounting for about 70%-80% of the total number of tumors.

Over the past decade, the incidence of lung cancer has gradually increased, but the incidence of several cancers has dropped significantly: gastric cancer, esophageal cancer, and liver cancer have decreased.

These three tumors are all highly lethal tumors. Their decline means that the risk factors of gastric cancer, esophageal cancer, and liver cancer to human life and health have decreased. So what is the reason for the decline in the incidence of these tumors?

First, I think it is the improvement of living standards.

Take stomach cancer and esophageal cancer, for example. They are mainly caused by malnutrition. Poor nutrition may lead to these tumors.

Second, there is the problem of pollution in food and drinking water.

Third, infection. The cause of gastric cancer infection is Helicobacter pylori.

In China, about 60% of people have been infected with Helicobacter pylori. Helicobacter pylori is one of the most important factors causing gastric cancer, and the World Cancer Center has classified it as a "Class I carcinogen." However, due to improved living habits, the incidence of these tumors has decreased.

So why has the incidence of liver cancer decreased? Speaking of liver cancer, in fact, liver cancer has a lot to do with "eating". In the southeastern coastal areas and Guangxi, the incidence of liver cancer is quite high; in addition, the high incidence of liver cancer is also related to the humid climate. The humid climate makes some foods prone to produce aflatoxin, which can also cause liver cancer. In China, liver cancer is mainly caused by hepatitis B, and the positive rate is about 15%.

In the late 1980s and early 1990s, hepatitis B virus immunization was popularized for newborns in China, which also led to a decrease in the incidence of liver cancer. In addition, with changes in our nutrition and food storage methods and the popularization of refrigerators, the incidence of liver cancer has shown a downward trend.

The incidence rates of gastric cancer, esophageal cancer, and liver cancer are decreasing. So, what tumors are increasing in China?

In China, the incidence of tumors is increasing, and the first is breast cancer in women, which is increasing very rapidly, increasing by about 60%-70% from 1988 to 2012.

The second fastest-rising disease is colorectal cancer. The incidence of colorectal cancer is related to the improvement of our living standards. Nutrition has increased, but people's physical activity has decreased.

In China, the places where colorectal cancer first increased were places with better living conditions, such as Zhejiang Province, which has always ranked among the top in colorectal cancer incidence rates.

The incidence of breast cancer and colorectal cancer is increasing. However, lung cancer has been increasing. The incidence of lung cancer in women has decreased slightly, but has not increased significantly. This trend is similar to that of the world.

In the past, Chinese people thought it was difficult to quit smoking, but now that health education has become more sound, the proportion of Chinese people who quit smoking has increased year by year. Lung cancer in women is a big problem. The key to this problem is that only 4% of women who suffer from lung cancer are smokers, and the vast majority of women who suffer from lung cancer are non-smokers.

Why do non-smoking women get lung cancer?

First, 50%-60% of Chinese men are smokers, and many women are forced to inhale secondhand smoke.

Second, in most rural areas in the north, women spend more time in the kitchen, and poor kitchen ventilation can easily cause lung cancer.

Third, outdoor air pollution. Outdoor air pollution is difficult to avoid and sometimes it is beyond personal control.

02 Differences in lung cancer risk factors between China and the United States and similarities and differences in the incidence of lung cancer among different ethnic groups

Ye Shuisong: Lung cancer is the most common cancer in China and the most common cancer in the United States. Are there any differences in the causes of lung cancer in the two major countries? In addition, are there any similarities or differences in the causes of lung cancer among different races?

**Zhang Zuofang: **In both China and the United States, lung cancer has a relatively high incidence rate among cancers.

First, smoking and secondhand smoke.

About 80%-90% of lung cancer is caused by smoking, and some lung cancer patients have tumors caused by passive smoking.

Second, air pollution.

In the United States, some basements are contaminated with radioactive substances, and occupational exposure at work may also cause lung cancer.

In terms of outdoor pollution, China's pollution level is higher than that of the U.S. In terms of indoor pollution, the smoking rate of American men and women is around 20%, and the passive smoking rate is relatively low; but the smoking rate of Chinese men can reach up to 70%, and is currently around 50%, which will cause passive smoking for women.

Third, the difference in cooking.

Americans are less likely to be polluted by cooking fume pollution because they mainly grill and boil when cooking, while Chinese people like to heat the oil pan, which produces light smoke, which itself is a carcinogen.

Fourth, genetic reasons.

From a genetic perspective, we have not yet found the pathogenic genes that are different for lung cancer in different ethnic groups, but genes do play a role in the carcinogenesis of lung cancer, especially genes related to nicotine receptors.

The increase in the proportion of lung cancer among Chinese women is actually mainly due to the increase in adenocarcinoma, which is related to genes. But there is also good news, there are now treatments specifically targeting this type of gene.

03 The relationship between aging and cancer

Ye Shuisong: At present, the aging population is increasing around the world, including in China. What do you think about the relationship between aging and cancer? Does the increase in aging also mean an increase in the number of cancer patients?

Zhang Zuofang: Except for childhood tumors, most tumors are closely related to aging. Abroad, many tumor patients are generally over 60 years old. There is a certain relationship between adult tumors and aging.

First, as age increases, the accumulated exposure dose becomes relatively greater.

For example, if a young person smokes a pack of cigarettes a day for 10 years, he is exposed for 10 years; if an older person smokes for 30 years, he is exposed for 30 years. Age itself is a variable of "exposure", which also increases the risk of cancer.

Second, the immune system of the elderly also declines after they become ill, and many physiological mechanisms in the body may cause tumors, such as the level of hormones produced in the body, the level of immunity in the body, and many changes in the body and metabolism, which contribute to the increase of some tumors.

04 Impact of the epidemic on cancer patients around the world, including those in China and the United States

Ye Shuisong: The epidemic is gradually fading around the world, which has made us focus again on the cancer patient group. What do you think about the impact of the epidemic on cancer patients around the world, including those in China and the United States?

Zhang Zuofang: The epidemic has a considerable impact on cancer, and this is the same all over the world.

First, it is the impact on cancer treatment.

Many cancer patients were unable to enter the hospital and receive proper treatment due to the epidemic, and many of them eventually died.

The same is true in the United States, where doctors cannot see patients, perform surgery, enter hospitals, or prescribe drugs. As a result, the five-year survival rate for cancer has dropped significantly.

We usually say that (cancer) "1/3 can be prevented, 1/3 can be detected early, and the remaining 1/3 can be treated." The epidemic has caused the "1/3 that can be treated" to leave us prematurely.

Second, it is impossible to perform early screening for cancer.

The goal of early screening is to detect early symptoms of cancer. Generally speaking, the survival rate of early-stage cancer and late-stage cancer after timely treatment is completely different.

To give a simple example, the five-year survival rate of early breast cancer (stage 0 or stage Ia) can reach over 90%. After proper surgery and treatment, its mortality rate will not be that high.

Another successful example in China is cervical cancer screening. In the past, cervical cancer screening could be done by cervical smears, and now there is HPV screening, which can detect early pathology earlier. The characteristic of cervical cancer is that it can not only detect early pathology, but also precancerous pathology. After precancerous pathology is discovered, it can be treated early, and basically it is unlikely to develop into invasive tumors.

However, due to the epidemic, large-scale, small-scale, and clinical cancer screenings have basically been suspended.

Third, during the epidemic, many people’s living habits have changed greatly.

It's not just lifestyle habits, but also other aspects of the impact.

To give a simple example, whether you are a smoker or a non-smoker, the possibility of smoking increases significantly when you are locked up at home, and the same goes for drinking.

In foreign countries, people who are locked at home can use some illegal drugs. Being locked at home also means that you cannot go out for physical exercise, and not having enough physical activity can also cause changes in some tumor risk factors.

As for diet, if we stay at home, we may not be able to have a balanced diet and may eat some unhealthy foods, which will also have an impact.

In addition, being locked down at home during the epidemic may cause some stress and depression, which are related to cancer. Therefore, the epidemic has a considerable and far-reaching impact on cancer.

05 Recommendations for reducing cancer risk

Ye Shuisong: What suggestions do you have for reducing the incidence of cancer? How can we curb the rapid increase in the number of cancer patients?

**Zhang Zuofang: **First, quit smoking. For lung cancer, I think smokers should quit smoking. The good news is that as long as you quit smoking early, the probability of getting cancer will decrease. Smoking does not only cause lung cancer, it can cause 16 different tumors, including oral cancer, laryngeal cancer, pharyngeal cancer, esophageal cancer, pancreatic cancer, stomach cancer, liver cancer, kidney cancer, bladder cancer, and leukemia.

The probability of smoking causing cancer is very high, so people who don’t smoke should never start, and people who already smoke should quit as soon as possible.

Smoking can also cause heart disease, stroke, diabetes, and comprehensive obstructive pulmonary disease, which we used to call "chronic bronchitis."

Is smoking related to breast cancer and colorectal cancer? The relationship between smoking and breast cancer is still controversial, but there is still a certain relationship between smoking and colorectal cancer.

Second, reduce indoor air pollution. Try to reduce the habit of deep-frying, pan-frying, or cooking with too much oil smoke. When cooking, you can pour some oil, put the vegetables in, add some water, and cover the pot. This is relatively healthier.

Third, a reasonable diet. A reasonable diet is very important. Diet is closely related to breast cancer and colorectal cancer. A reasonable diet means "reducing the amount of fat, increasing the amount of protein, increasing the amount of fiber, and reducing the amount of sugar."

For example, the increase of fiber can make the bowel movement smoother. Many patients with colorectal cancer have symptoms of constipation. There are some chemicals in the feces in the large intestine that can cause cancer, so increasing intestinal peristalsis can reduce the incidence of cancer.

In addition, fat should not be too high, as high fat also has a great impact on cancer. But so far, we have not made a summary conclusion about fat, and we can conclude that "fat must cause cancer". Reducing fat is definitely beneficial to people. After increasing fat, weight will also increase, and obesity can also cause tumors, so the diet should be adjusted to "low sugar, high fiber, high protein, low fat".

Why are there so many diabetics in China and why do their blood sugar levels rise so quickly? This has something to do with eating rice. So it is recommended to use rice and steamed bread as complementary foods, and eat more vegetables and high-protein fish and shrimp. It is best to eat white meat (fish, shrimp, chicken), eat less red meat (pork, beef, lamb), increase protein intake, and reduce the incidence of cancer through a reasonable diet.

Fourth, avoid excessive drinking. Alcohol can cause many tumors, such as breast cancer and colorectal cancer.

When I was participating in the World Health Organization's expert group on alcohol and cancer research, I and other experts confirmed at the discussion meeting that there is a very strong correlation between breast cancer, colorectal cancer and drinking.

So far, all alcohol, including red wine, is a major cause of cancer. The more you drink, the greater the risk. So it is best not to drink alcohol. If you really have to drink, try to limit it to a small glass of red wine a day.

Fifth, we need to pay attention to physical activities. If you do a lot of physical activities every day, you don’t actually need to exercise. But now there are many white-collar workers sitting in front of the computer for eight hours without moving much, and after get off work they eat, drink, and sleep. This kind of work and rest is actually not good for people.

We'd better make sure we have at least 40 minutes of physical activity every day. Swimming, walking, running, playing basketball are all good exercises. If you are older, you can choose jogging or walking.

Finally, it is necessary to maintain mental happiness. Mental health is very important, and optimism is also a good medicine for curing diseases.