What is Cancer?

We tend to think of cancer as a single, highly dangerous disease.

In truth, there are as many types of cancers as there are types of cells in the body. That’s because cancer is, at its most basic level, a condition where a particular type of cell—breast, prostate, colon, blood, even fat—begins to grow and replicate at a faster rate than it should.


How Cancer Begins

The abnormal cell growth that is typical of all formers of cancer is the result of damage to that cell’s DNA (the complex sequence of genetic instructions inside each cell that determine what type of cell it becomes, how fast it grows, and how often it replicates). Sometimes the body can repair this damage on its own. Sometimes, the damage is so severe that the cell simply dies. In cancer, somehow that damaged cell survives and continues making more damaged cells—which in turn make even more.


How Cancer Makes You Ill

As these abnormal cells multiply, they often begin to crowd out normal cells in other tissues, which makes it difficult for those other tissues to function the way they are supposed to, forming what we call a tumor (a swelling of the body caused by abnormal tissue growth).

In some forms of cancer, such as various forms of leukemia (cancer of the blood cells), the cancer cells don’t form a tumor. Instead, healthy blood cells are overwhelmed by an influx of cancerous blood cells, which cannot do the work of carrying oxygen and nutrients and removing waste from the rest of the body.


Learn More about Cancer

If you’re looking for trustworthy and up-to-date information about various forms of cancer, we recommend the following resources:

National Cancer Institute at the National Institutes of Health – this federally funded research center offers a wealth of information, from defining basic terms to information about rare conditions to the latest research developments.

Mayo Clinic – This highly regarded hospital maintains a library of health information, including easy-to-understand information about cancer causes, prevention, symptoms and treatment options.

M.D. Anderson Cancer Center – The top-ranked cancer hospital in the United States, M.D. Anderson is an excellent source of information about clinical trials, research breakthroughs and the basics about virtually every form of cancer.

American Cancer Society – Find statistics on cancer diagnosis and survival rates in every state, learn about cancer prevention and detection, and find support programs for patients going through treatment.