Cancer is a disease that occurs when cells grow uncontrollably and spread to other parts of the body. Cancer can start in almost any tissue or organ in the body. There are more than 100 different types of cancer.

Cancer is caused by changes in DNA. DNA is the genetic material that controls how our cells grow and function. These changes can be caused by a variety of factors, including:

* **Smoking:** Smoking is the leading cause of preventable death in the United States and is responsible for about 30% of all cancer deaths. Smoking can cause cancer of the lung, bladder, cervix, colon and rectum, esophagus, kidney and ureter, larynx, liver, mouth and throat, pancreas, stomach, and myeloid leukemia.
* **Sun exposure:** Sun exposure is the leading cause of skin cancer, the most common type of cancer in the United States.
* **Genetics:** Some cancers are caused by inherited genetic changes. For example, breast cancer can be caused by mutations in the BRCA1 and BRCA2 genes.
* **Viruses and bacteria:** Some viruses and bacteria can cause cancer. For example, the human papillomavirus (HPV) can cause cervical cancer and the hepatitis C virus can cause liver cancer.
* **Environmental toxins:** Exposure to environmental toxins, such as asbestos, benzene, and formaldehyde, can increase the risk of cancer.

The symptoms of cancer vary depending on the type and location of the cancer. Some common symptoms of cancer include:

* **Unexplained weight loss**
* **Fatigue**
* **Fever**
* **Night sweats**
* **Pain**
* **Lumps or bumps**
* **Changes in skin color**
* **Changes in bowel habits**
* **Difficulty breathing**
* **Unusual bleeding or discharge**

If you are experiencing any of these symptoms, it is important to see a doctor right away.

Cancer can be treated with a variety of methods, including surgery, chemotherapy, radiation therapy, and targeted therapy. The best treatment for cancer depends on the type and stage of the cancer.

Cancer is a serious disease, but it is important to remember that there are many people who have survived cancer. With early detection and treatment, many cancers are curable.