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What is cancer and what causes cancer?

What is cancer and what causes cancer?

Cancer is a group of diseases that cause cells in the body to change and grow out of control. Cancer begins when genetic changes interfere with the orderly process of cell growth. Cells start to grow uncontrollably, forming a mass called a tumor. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can grow and invade nearby tissues. A benign tumor means it cannot grow and invade nearby tissues.

Cancerous tumors can also spread to other parts of the body through the bloodstream or lymphatic system. This process is called metastasis.

There are more than 100 types of cancer. Some common types include breast cancer, lung cancer, colon cancer, prostate cancer, and skin cancer

Signs and symptoms

There are many different types of cancer, and the signs and symptoms can vary depending on the type and location of the cancer. However, some general signs and symptoms of cancer include:

  • Fatigue

  • Loss of appetite

  • Unexplained weight loss

  • Pain

  • Changes in bowel or bladder habits

  • Skin changes

  • Sores that do not heal

  • Cough or hoarseness that does not go away


Cancer is caused by changes to the DNA inside of cells. These changes can be inherited, or they can occur during a person’s lifetime. The changes cause the cells to grow and divide out of control, which can form a tumor.

Risk factors

Cancer can occur at any age, but the risk of developing cancer increases as you age. The American Cancer Society’s estimates for cancer in the United States for 2019 are:

  • About 1,762,450 new cases of cancer will be diagnosed.
  • About 606,880 people will die from cancer.
  • Approximately 1 in 8 women in the United States will develop breast cancer at some point in their lives.
  • Approximately 1 in 8 men in the United States will develop prostate cancer at some point in their lives.

Cigarette smoking is the most important preventable cause of cancer in the world. Tobacco use is responsible for about 22% of cancer deaths.

Other risk factors for cancer include:

  • Exposure to radiation

  • Certain chemicals and industrial products

  • Certain viruses and bacteria

  • Family history of cancer

  • Unhealthy diet

  • Obesity

  • Lack of physical activity

  • Excessive alcohol use

  • Exposure to cancer-causing substances

  • Certain medical conditions

  • Exposure to ultraviolet radiation


There is no sure way to prevent cancer, but there are things that you can do to lower your risk. These include:

  • Not smoking

  • Limiting alcohol consumption

  • Eating a healthy diet

  • Staying at a healthy weight

  • Getting regular physical activity

  • Protecting your skin from the sun

  • Getting vaccinated against certain infections

  • Avoiding exposure to cancer-causing substances


If you have any signs or symptoms of cancer, it is important to see a doctor right away. They will likely perform a physical exam and order some tests, such as blood tests, X-rays, or a biopsy. A biopsy is the only way to definitively diagnose cancer.


If you have cancer, treatment will depend on the type of cancer, where it is located, and how advanced it is. Treatment options include:

  • Surgery

  • Radiation therapy

  • Chemotherapy

  • Targeted therapy

  • Immunotherapy

Coping and support

Cancer can be a difficult diagnosis to cope with. You may feel scared, angry, or helpless. You may also have physical symptoms that make it hard to cope with your diagnosis. It is important to find a support system to help you through this time.

There are many ways to cope with cancer. Some people find support groups helpful. Others find comfort in religion or spirituality. Some people find that talking with a counselor or therapist helps them cope.


Cancer can have many different complications, such as pain, fatigue, financial problems, and emotional distress. It is important to talk to your doctor about ways to manage these complications.

Living with cancer

If you have cancer, it is important to follow your treatment plan and see your doctor for regular checkups. It is also important to make healthy lifestyle choices, such as eating a healthy diet and exercising regularly. These choices can help you feel your best and improve your quality of life.