For cancer to develop, all cells need more than the ability to divide and grow uncontrollably. Non-cancerous, benign tumors also undergo that process. What is ultimately crucial is their ability to invade outside their localized area. The cells in any given area are tightly attached to each other, forming a natural guard against invasion. So for a cell to break outside of its own area and into another area requires special qualities.
One of the things being studied now in terms of cancer is that tight cell connection. There is a kind of special "glue" called the extracellular matrix which holds cells together. If a cell has a substance that can dissolve or consume the "glue", it will have a much better chance of getting out of its area and into another.
The ability of a cancer cell to invade may be caused by several factors. One of these is the ability to release a protein, known as metalloproteinase that functions to dictate the cell connections not to adhere to each other so tightly. Then the other cells behave in a way that allows the cancer cell to escape its territory and invade. Another possibility is that the cancer cell may be able to push its way out of the tight cell connection on its own. There are a lot of ways this might happen. In the long run, that is good because there are a lot of potential ways to interfere with this process. The down side of it is, it's difficult in the short run because this makes these complicated to figure out.
With the discovery of various cancer genes came a new way of thinking about breast cancer. The astonishing part of it is that all these years, cancer cells have been studied by looking at them in isolation. Medical researchers take cancer cells and grow them in petri dishes and then study their behavior. This is like placing criminals in isolation chambers and then studying their personalities. They're not interacting with anyone, so there actually is no way to examine how they behave. We have finally realized that if we were to study cancer cells seriously in their own environment we can learn much more, because they interact with their surrounding cells and the surrounding cells have an effect on them.
A medical researcher in Berkeley, California, has begun studying cancer cells in a breast tissue environment. She took breast cancer cells that have genetic mutations and grew them in a cell culture or normal breast extracellular matrix. In that environment the cancer cells behaved like normal cells - they proliferated and grew breast ducts and did other things that healthy breast cells do. The influence of healthy normal cells surrounding the cancer cells caused them to function in a normal way, even though they were already genetically altered.
This means that, if the right tools were found, cancer may be reversible, or at least be controlled to some extent and we won't have to try to kill every last cancer cell.
