Causes of Cancer

21.03.2024

WHAT ARE THE CAUSES OF CANCER?

Cancer risk factors refer to various factors that play a role in the development of cancer. These include genetic predisposition, lifestyle choices, and environmental exposures. Being aware of cancer risk factors and making healthy lifestyle choices are important steps in reducing cancer risk.

Cancer is a complex disease that occurs as a result of the combination of many factors. The main reasons are:

GENETIC FACTORS

Cancer may develop due to some genetic mutations. Genetic risk factors for cancer are more common in individuals with a family history of cancer, and in some cases, genetic changes that increase the risk of cancer are inherited. Some examples are:

BRCA1 and BRCA2 Gene Mutations: These genetic mutations significantly increase the risk of breast and ovarian cancer, especially in women. BRCA mutations have also been linked to other types of cancer such as pancreatic, prostate and melanoma.

Lynch Syndrome:Mutations in the MLH1, MSH2, MSH6, PMS2, and EPCAM genes increase the risk of colon, endometrial, and other types of cancer (stomach, pancreas, urinary tract, or brain).

CDH1 Gene Mutation: Mutation in the CDH1 gene is associated with the risk of hereditary diffuse gastric cancer and breast cancer.

PALB2 Gene Mutation:An inherited mutation in the PALB2 gene increases the risk of breast cancer and, in some cases, may occur in families with more than one case of pancreatic cancer.

STK11 Gene Mutation: Mutations in the STK11 gene cause Peutz-Jeghers syndrome, and in this case, people are at risk of breast, cervix, ovarian, gastrointestinal tract and pancreatic cancers.

These are just a few examples of the role genetic factors play in cancer risk. For genetic changes to cause cancer, cells must change the way they grow and spread. Most cases of cancer occur as a result of a lifetime of accumulation of genetic changes. Having genetic changes that pose a risk of cancer does not necessarily mean that you will get cancer; However, people with these changes have an increased risk of developing cancer.

It is important for individuals with a family history of cancer to evaluate their risk through genetic counseling and, if necessary, genetic testing. Genetic testing can identify the presence of genetic changes that increase cancer risk and lead to early diagnosis and preventive treatment strategies. Additionally, environmental factors and lifestyle changes may reduce the risk of cancer development in individuals with high cancer risk due to genetic mutations.

Image 1. Genetic factors have a high impact on cancer development.

ENVIRONMENTAL FACTORS AND LIFESTYLE FACTORS:

Environmental factors play an important role in the development of cancer. These include exposure to ultraviolet rays, radiation, air pollution and harmful chemicals. Smoking, excessive alcohol consumption, unhealthy eating habits and lack of physical activity can increase the risk of cancer.

Cigarette: The relationship between smoking and cancer development is well proven by medical research and health studies. Smoking is a leading cause of many types of cancer, especially lung cancer. Cigarette smoke contains many carcinogenic substances, and these substances have the potential to damage DNA, which can lead to genetic mutations and, ultimately, the development of cancer.

The types of cancer caused by smoking are not limited to lung cancer. The risk of developing other types of cancer, such as cancer of the mouth, larynx, esophagus, pancreas, bladder, kidney and even the cervix, also increases in smokers. Smoking may also contribute to mechanisms that make it easier for cancer cells to spread throughout the body and reduce the immune system's ability to defend against cancer.

The harms of smoking are directly proportional to the amount and duration of smoking; Smoking more and smoking for longer increases the risk of cancer. However, quitting smoking reduces the risk of cancer and supports the body's self-healing process. Even after quitting, former smokers continue to have a higher risk of developing certain types of cancer than people who have never smoked, but this risk decreases over time.

It is important to raise awareness of the health effects of smoking and encourage individuals to quit smoking. Quitting smoking is an effective step in preventing many serious health problems, including cancer.

Alcohol Consumption: Excessive alcohol consumption increases the risk of cancer, especially liver, mouth, throat and breast cancer. The relationship between alcohol consumption and cancer development is supported by various scientific studies. Alcohol is a risk factor that contributes to the development of many types of cancer, especially liver cancer.

The carcinogenic effect of alcohol is associated with the chemicals that are formed when it is metabolized in the body and the potential of this process to damage cells and DNA. Alcohol is linked to many types of cancer, especially cancers of the mouth, esophagus, larynx, liver and breast. The harmful effects of alcohol are directly proportional to the amount consumed; that is, the risk increases with increasing alcohol consumption. Alcohol's negative effects on the immune system can also increase the risk of cancer. Alcohol can reduce the body's ability to fight infections and potentially cancerous cells. In addition, alcohol consumption can make the body vulnerable to other carcinogenic substances.

Reducing alcohol consumption is among the strategies to reduce cancer risk. Limiting or stopping alcohol consumption can help prevent many health problems, including cancer. For this reason, healthcare professionals and public health organizations encourage individuals to inform them about the possible harms of alcohol consumption and to make healthy lifestyle choices.

Image 2. There are many environmental factors that play a role in cancer development.

Infections: Some viruses and bacteria can cause cancer. For example, human papillomavirus (HPV) can cause cervical cancer, and Helicobacter pylori bacteria can cause stomach cancer.

Some infections that lead to the development of cancer include:

Human Papillomavirus (HPV): HPV can cause anal, vaginal, vulvar, penile and oropharyngeal (mouth and throat) cancers, especially cervical (cervix) cancer.

Hepatitis B and C Viruses (HBV and HCV): Chronic HBV or HCV infections can cause liver cancer. HCV may also increase the risk of non-Hodgkin lymphoma.

Epstein-Barr Virus (EBV): EBV may increase the risk of Burkitt lymphoma, Hodgkin and non-Hodgkin lymphomas, and stomach cancer.

Human İmmunodeficiency Virus (HIV): HIV itself does not directly cause cancer, but it weakens the immune system and may allow other oncoviruses to cause cancer. HIV-associated cancers include Kaposi sarcoma, Hodgkin and non-Hodgkin lymphoma, cervical cancer, and cancers of the anus, liver, mouth, throat, and lung.

Human Herpesvirus 8 (HHV-8): HHV-8 can cause Kaposi's sarcoma, especially in people with weakened immune systems.

Helicobacter pylori (H. pylori): H. pylori can cause MALT lymphoma, a type of lymphoma on the stomach lining.

Opisthorchis viverrini or Schistosoma haematobium: These parasites may increase the risk of bile duct cancer and bladder cancer, respectively.

Since many of these infections can lead to serious health problems, prevention and early diagnosis are important. For example, vaccines against HPV are available and cervical cancer can be detected early with regular screening tests. Similar preventive strategies and treatments are available for other infections.

Hormonal Factors: Some types of cancer, especially breast and prostate cancer, are related to hormone levels in the body.

Hormonal factors that lead to cancer development are associated with the role of hormone balances in the body and biological processes related to hormones. Important hormonal factors include:

Estrogen and Progesterone: These two female sex hormones are known to play a role in the development of breast and endometrial cancers. Long-term and/or high levels of exposure to these hormones may increase the risk of breast cancer. For example, early menstrual onset and late menopause increase risk by causing longer exposure to these hormones.

Menopausal Hormone Therapy: Postmenopausal hormone therapy containing a combination of estrogen and progestin may increase the risk of breast cancer. Menopausal hormone therapy containing estrogen may increase the risk of endometrial cancer in women who have not had a hysterectomy.

Hormonal Contraceptives and Cancer Risk: A slight and transient increase in the risk of breast cancer has been observed with the use of hormonal contraceptives. But hormonal contraceptives may also reduce the risk, especially of ovarian cancer and endometrial cancer.

Reproductive Factors and Cancer: Reproductive factors such as birth date, parity and breastfeeding also have an impact on hormonal balances and may therefore affect the risk of some types of hormone-related cancers.

These factors are part of hormonal balances that can affect an individual's risk of developing cancer. Understanding the relationship between hormones and cancer plays an important role in the development of cancer prevention and early detection strategies.

Age: In general, the risk of cancer increases with age. This may be due to the accumulation of DNA damage in cells and decreased immune functions associated with age. Age is one of the most important factors for cancer risk. Cancer diagnosis rates increase with age. For example, the rate of cancer diagnoses in people under 20 is less than 25 per 100,000 people, while the rate for people 60 and older is more than 1,000 per 100,000 people. The median age at diagnosis of cancer is 66 years. This means that half of cancer cases occur in people under this age and half in people over this age. For example, the median age at diagnosis for breast cancer is 62, 67 for colorectal cancer, 71 for lung cancer, and 66 for prostate cancer. However, cancer can be diagnosed at any age; for example, bone cancer is most often diagnosed during childhood and adolescence

Image 3. Smoking can be considered the most important preventable risk factor in the development of cancer. It is associated with 13 known types of cancer.

Nutrition and Diet: Some foods and dietary habits are thought to increase the risk of cancer, such as high-fat diets and consumption of processed meat. The relationship between nutrition and cancer is the focus of many studies and various findings have been obtained on this subject. 

Fruits and vegetables: It has been found that high consumption of fruits and vegetables can reduce the risk of stomach cancer. Diets with particularly high vitamin C concentrations may be effective in this regard. One study observed that β-carotene, selenium, and α-tocopherol supplementation resulted in a significant reduction in gastric cancer mortality.

Red and Processed Meat: Consumption of red and processed meat has been found to be positively associated with the risk of colorectal cancer. In 2015, IARC classified processed meat as carcinogenic to humans, and it was stated that daily consumption of 50 grams of processed meat increased the risk by 17%.

Milk and Calcium: Consumption of milk and calcium has been found to moderately reduce the risk of colorectal cancer. Calcium may play a protective role by forming complexes with secondary bile acids and heme in the intestinal lumen.

Dietary Fibers and Whole Grains: In the 1970s, it suggested that low rates of colorectal cancer in some parts of Africa were associated with high dietary fiber consumption. Prospective studies have shown that consuming 10 grams more total dietary fiber per day reduces the risk of colorectal cancer by an average of 10%.

Folic acid: High dietary folate intake has been associated with a reduced risk of colorectal cancer. However, high folate status may promote the growth of colorectal tumors, and no definitive conclusion has been reached on this issue.

General Lifestyle: In addition to diet, physical activity and maintaining a healthy body weight are also important in the fight against cancer. Lifestyle choices have been shown to influence cancer risk, and approximately one-third of cancer deaths are linked to lifestyle behaviors such as diet and physical activity.

This information provides an overview of the relationship between nutrition and cancer. However, research on this subject is ongoing and individual, genetic and environmental factors are also important in reducing the risk of cancer. Therefore, it is important to consult with a healthcare professional before making any dietary changes.

Sedentary Life:  Lack of physical activity may increase the risk of developing some types of cancer. Physical activity plays an important role in the development of cancer because it improves the general health of the body and has a protective effect against many types of cancer. Regular exercise reduces inflammation levels in the body, strengthens the immune system and improves hormone balance. In particular, it is effective in preventing obesity-related types of cancer because physical activity helps maintain a healthy body weight, thereby reducing cancer-related risk factors. Additionally, exercise can speed up bowel movements, allowing potential carcinogenic substances to pass through the digestive system more quickly. The combination of these effects makes physical activity an important factor in reducing cancer risk. Therefore, regular physical activity is considered an important part of a healthy lifestyle and is seen as an effective method of reducing the risk of cancer.

Chronic Diseases: Long-term inflammation can increase the risk of developing cancer. Some chronic diseases, especially inflammatory diseases and some chronic viral infections, can increase the risk of cancer. The relationship between chronic diseases and cancer development can occur through both direct and indirect pathways, and this relationship involves complex interactions. Chronic diseases often lead to increased levels of inflammation in the body, hormone imbalances and metabolic changes. These conditions can pave the way for abnormal growth of cells and the development of cancer. For example, Type 2 diabetes and obesity may increase the risk of some types of cancer through insulin resistance and chronic inflammation. Additionally, chronic diseases can weaken the immune system, reducing the body's defenses against cancer cells. In conditions such as hypertension and heart diseases, it can increase oxidative stress in the body, causing DNA damage and abnormal behavior of cells. The combination of these factors indicates that chronic diseases can have direct and indirect effects on cancer development. Therefore, management and treatment of chronic diseases is considered an important factor in reducing cancer risk.

Although each of these factors increases the risk of cancer, more than one factor must often be present for the development of cancer. Additionally, although everyone is exposed to these risk factors, it does not mean that everyone will not develop cancer; The complex interaction of genetic and environmental factors is important in this regard. Cancer prevention and early detection are critical to manage these risk factors and prevent or detect cancer development early.

Resources:

https://www.cancer.org/cancer/risk-prevention/genetics.html

https://www.cancer.gov/about-cancer/causes-prevention/genetics

https://www.cancer.gov/about-cancer/causes-prevention/risk/infectious-agents

https://www.mdanderson.org/publications/focused-on-health/7-viruses-that-cause-cancer.h17-1592202.html

https://www.cancer.org/cancer/risk-prevention/infections/infections-that-can-lead-to-cancer.html

https://www.cancer.gov/about-cancer/causes-prevention/risk/age

https://www.cancer.gov/about-cancer/causes-prevention/risk/hormones

https://www.cancerresearchuk.org/about-cancer/what-is-cancer/body-systems-and-cancer/the-hormone-system-and-cancer

https://canceratlas.cancer.org/risk-factors/hormones/

https://www.communitycancercenter.org/nutrition/the-relationship-between-nutrition-and-cancer/

https://www.bmj.com/content/368/bmj.m511