Cancer is a disease where cells in the body grow out of control and can form harmful lumps called tumors. Normally, your body's cells grow, divide, and die in an orderly way, like a well-organized construction project. But cancer cells ignore these rules. They multiply rapidly, don't die when they should, and can spread to other parts of the body, interfering with how organs work.

There are many types of cancer, named for where they start: lung cancer, skin cancer, leukemia (blood cancer), and many others. What makes cancer dangerous is that these abnormal cells crowd out healthy cells and steal nutrients the body needs for normal functions.

Doctors treat cancer with surgery, radiation, chemotherapy, and other methods. Modern medicine has made tremendous progress: many cancers that were once deadly can now be cured or controlled, especially when caught early. Scientists continue working to develop better treatments and find cures.

Sometimes people say something is “like a cancer” to mean it's spreading harmfully through an organization or system, similar to how the disease spreads through the body.