Cancer 101 - What Is Cancer?

How does cancer grow?

This is a picture of skin tissue showing how cancer develops.

• Tissue Square 1 (top left) When a normal cell dies, your body replaces it with another normal cell. (pink colored cell)
• Tissue Square 2 (middle square) Cancer cells grow in an uncontrolled manner. They fail to die and therefore the diseased cells accumulate and form a mass or "tumor". (green colored cell)
• Tissue Square 3 (bottom, right) One malignant cell becomes two, two become four, four become eight, and so on, until a mass of cells (a tumor) is created.

Cancer cells invade nearby tissue and/or blood vessels. This is a necessary step for them to metastasize or spread to other organs.

Tumors remain small until they're able to attract their own blood supply (angiogenesis), which allows them to obtain the oxygen and nutrients they need to grow larger.

Cancer can take decades to develop. By the time a cancerous mass is detected, it's likely that 100 million to 1 billion cancer cells are present, and the original cancer may have been dividing for five, ten or even more years.