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11.56: Carcinogens and Cancer

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    Why is tanning bad for your health?

    It might be fun to lay out in the sun like these two girls are doing. But getting too much sun can be very dangerous. Overexposure to sunlight raises your risk for skin cancer.


    Cancer is a disease that causes cells to divide out of control. Normally, the body has systems that prevent cells from dividing out of control. But in the case of cancer, these systems fail. Cancer is usually caused by mutations. Mutations are random errors in genes. Mutations that lead to cancer usually happen to genes that control the cell cycle. Because of the mutations, abnormal cells divide uncontrollably. This often leads to the development of a tumor. A tumor is a mass of abnormal tissue. As a tumor grows, it may harm normal tissues around it. Anything that can cause cancer is called a carcinogen. Carcinogens may be pathogens, chemicals, or radiation.


    Pathogens that cause cancer include the human papilloma virus (HPV) (Figure below) and the hepatitis B virus. HPV is spread through sexual contact. It can cause cancer of the reproductive system in females. The hepatitis B virus is spread through sexual contact or contact with blood containing the virus. It can cause cancer of the liver.

    The human papilloma virus can cause cancer
    Figure \(\PageIndex{1}\): The mutations that cause cancer may occur when people are exposed to pathogens, such as the human papilloma virus (HPV), which is shown here.


    Many different chemical substances cause cancer. Dozens of chemicals in tobacco smoke, including nicotine, have been shown to cause cancer (Figure below). In fact, tobacco smoke is one of the main sources of chemical carcinogens. Smoking tobacco increases the risk of cancer of the lung, mouth, throat, and bladder. Using smokeless tobacco can also cause cancer. Other chemicals that cause cancer include asbestos, formaldehyde, benzene, cadmium, and nickel.

    Cigarettes are a major source of chemical carcinogens
    Figure \(\PageIndex{2}\): The mutations that cause cancer may occur when people are exposed to chemical carcinogens, such as those in cigarettes. It can be argued that tobacco smoke is the main source of chemical carcinogens.


    Forms of radiation that cause cancer include ultraviolet (UV) radiation and radon (Figure below). UV radiation is part of sunlight. It is the leading cause of skin cancer. Radon is a natural radioactive gas that seeps into buildings from the ground. It can cause lung cancer.

    Figure \(\PageIndex{3}\): The mutations that cause cancer may occur when people are exposed to radiation, including the radiation from sunlight.

    Common Types of Cancer

    Cancer is usually found in adults, especially in adults over the age of 50. The most common type of cancer in adult males is cancer of the prostate gland. The prostate gland is part of the male reproductive system. Prostate cancer makes up about one third of all cancers in men. The most common type of cancer in adult females is breast cancer. It makes up about one third of all cancers in women. In both men and women, lung cancer is the second most common type of cancer. Most cases of lung cancer happen in people who smoke.

    Cancer can also be found in children. But childhood cancer is rare. Leukemia is the main type of cancer in children. It makes up about one third of all childhood cancers. It happens when the body makes abnormal white blood cells.

    Sometimes cancer cells break away from a tumor. If they enter the bloodstream, they are carried throughout the body. Then, the cells may start growing in other tissues. This is usually how cancer spreads from one part of the body to another. Once this happens, cancer is very hard to stop or control.

    Treating Cancer

    If leukemia is treated early, it usually can be cured. In fact, many cancers can be cured, which is known as remission, if treated early. Treatment of cancer often involves removing a tumor with surgery. This may be followed by other types of treatments. These treatments may include drugs (known as chemotherapy) and radiation therapy, which kill cancer cells.

    The sooner cancer is treated, the greater the chances of a cure. This is why it is important to know the warning signs of cancer. Having warning signs does not mean that you have cancer. However, you should see a doctor to be sure. Everyone should know the warning signs of cancer. Detecting and treating cancer early can often lead to a cure. Some warning signs of cancer include:

    • Change in bowel or bladder habits.
    • Sores that do not heal.
    • Unusual bleeding or discharge.
    • Lump in the breast or elsewhere.
    • Chronic indigestion.
    • Difficulty swallowing.
    • Obvious changes in a wart or mole.
    • Persistent cough or hoarseness.


    • Cancer is caused by mutations, which can be caused by pathogens, chemicals, or radiation.
    • Cancer can be treated with surgery, drugs, and radiation.

    Explore More

    Use the resources below to answer the questions that follow.

    Explore More I

    1. How are genetic mutations thought to affect the formation of cancer? What is the result of this process?
    2. Cancer cells continuously divide. How does this affect the mutation rates of the cells?
    3. What is angiogenesis? How does this help cancer spread?


    1. Define carcinogen and give three examples.
    2. Explain how mutations can lead to cancer.
    3. What type of cancers are associated with chemicals in cigarettes?
    4. What type of cancer may be caused by UV radiation?
    5. List four signs of cancer.

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