Cancer is a common disease throughout the world, and nearly everyone knows someone who has had it. In the United States, cancer affects one in three people and is the second leading cause of death after heart disease. Cancer is commonplace enough that fundraisers for specific types of cancer are held throughout the year and often supported by large companies and sports franchises. Despite its prevalence, many people don’t understand exactly what cancer is and how it develops.
What is cancer?
The body is made up of more than 100 million cells, and each cell contains instructions on how to grow, what functions it will serve, how to reproduce, and when to die. Most cells follow those instructions very well. Those instructions are contained in a person’s DNA, which is the genetic code that tells cells how to behave. However, when a change in or damage to a person’s DNA happens, cells stop following those instructions. DNA damage can be done by random mutations in the genes or by damage caused by exposure to things in our environment, such as cigarette smoke, alcohol, or ultraviolet (UV) radiation from the sun.
Normally, cells divide and replicate relatively slowly. However, cancerous cells, the ones that are no longer following their instructions, start replicating rapidly. Cancer cells replicate whenever they want, while normal cells need a specific signal to tell them to replicate. Cancer cells remain in a state called “immature” rather than growing into cells that have specific jobs or functions. They evade the immune system, so the body’s natural defenses can’t easily find and destroy them. Cancer cells don’t hang out with each other as normal cells do, so they can travel around the body through the bloodstream or the lymph nodes and cause cancer to start growing in various places around the body. They grow into other tissues and organs, which can cause serious damage.
Types of cancer
There are several hundred kinds of cancer, and cancer cells can impact any of the different tissues in the body, from organs to bones to blood and everything in between. While there are many individual kinds of cancer, they generally can be grouped into four main categories based on where the cancer gets started:
- Carcinomas: These begin in internal organs and glands and usually form a solid tumor. This is the most common type of cancer and can be in the prostate, breast, lung, or colon.
- Sarcomas: These begin in the body’s supportive and connective tissues, including muscles, fat, nerves, blood vessels, cartilage, or bones.
- Leukemias: These are blood cancers that are caused when healthy blood cells start to mutate and begin replicating in an out-of-control fashion.
- Lymphomas: These cancers begin in the lymphatic system, a network of vessels and glands that are designed to fight off disease and infection.
How does cancer spread?
Nearly all cancers begin in a specific part of the body, but they can travel to other parts of the body through blood vessels or the lymphatic system. Cancer cells do not like to stick together like normal cells do. Cancer cells must go through a process of breaking away from the initial tumor, attaching to the outside of a blood vessel or lymph node, and then crossing that wall to flow with the blood or lymph to travel. Cancer cells work hard for that journey so they can travel to other parts of the body. Wherever they end up, they continue to grow. The cancerous cells likely will begin to grow into parts of the body such as muscles, bones, and organs, which can cause new symptoms and complications.
When a person gets cancer, doctors use a numbering system to indicate the stage of cancer. The stages of cancer are I, II, III, and IV. If a person has stage I or II, cancer has not spread very far from the initial site. Stage III and IV means the spread is more extensive. The spread from one part of the body to another is called metastasis, and that means a doctor could refer to metastatic breast cancer that is found in the liver, brain, or elsewhere. It does not mean that a person has a new cancer of the liver or brain, but rather that the original breast cancer has spread to that part of their body.