What is Cancer Anyway? Here’s a Basic Definition
Our bodies are made up of cells. In a healthy body, these cells live out their happy lives doing all the things cells are supposed to do: They grow, divide, and at the end of their natural time, die, with a "next generation" of cells doing the same, replacing them. The cycle continues.
Cancer begins when cells refuse to adhere to their time-honored, traditional life cycle. Cancer cells are unwilling to die a natural death and instead continue to divide and grow. The new cells produced by this cellular division are also cancer cells. Another way cancer cells differ from their normal counterparts is that they have the ability to invade healthy cells and take them over, converting them to their cause. This allows cancer to migrate into healthy tissues and organs and set up shop.
After a while cancer cells can form tumors but in some cancers like Leukemia, cancer cells are present in the blood, blood forming organs, lymph or lymphatic system. When this occurs, the bloodstream becomes a super highway for cancer cells to migrate into healthy tissues or systems throughout the body, in a process called metastasis.
Types of cancer are named for their home towns, the sites in the body from which they originate. Cancer of the breast is called "breast cancer", but cancer that migrates from the breast to the bone is still breast cancer-metastatic breast cancer.
Each cancer has its own unique characteristics determining growth rate and symptoms, and each type responds to different treatments. Therefore, proper diagnosis is an important step to getting the right treatment.
For more information, check out Defining Cancer at the National Cancer Institute's website.