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Cancer: Cells behaving badly
Profile of a cancer cell
Even though every cancer is different, there’s a shared set of behaviors that characterizes all cancer cells:

Uncontrolled growth: Normal cells grow and divide when they get messages from the cells around them that it’s time to do so. Cancer cells, on the other hand, are able to jump-start growth by themselves, and therefore can divide and make new copies of themselves independent of what's going on in the cells around them.

Lack of response to stop signals: A healthy cell will stop dividing when one of two things happens: it receives signals from nearby cells that the “neighborhood” is crowded enough, or its cellular machinery is damaged. Ordinarily, a cell will take time out to repair problems. Cancer cells just keep on going, proliferating under conditions that would stop normal cells, and making new copies of cells with damaged DNA.

Immortality: Almost all the cells in your body are programmed to stop functioning or commit suicide when cellular machinery is damaged beyond repair, when they’re infected by a virus, when there are too many cells, or when cellular functions begin to break down. An aging cell may simply stop dividing, or it may undergo a sequence of events called programmed cell death or apoptosis. Cancer cells ignore these stop signals, and are thus able to expand their numbers.

Ability to divide infinitely: Healthy cells eventually stop dividing but continue to live. Their growth is stopped by the fact that their DNA is programmed to tolerate a certain number of replications, and sends a “stop” signal when it’s reached its limit. Cancer cells evolve new ways to evade these signals. As a result, they continue to replicate, producing new cells that have miscopied or mutated DNA strands

Recruiting a food supply: All cells need to be fed by oxygen and nutrients in the blood. Ordinarily, the body’s systems carefully regulate the growth of new feeder blood vessels, a process called angiogenesis. A tumor of cancerous cells typically skirts these systems and independently signals the body to feed it, causing new vessels to grow into the tumor. This vascularization of a tumor marks one of the defining moments when a precancerous tissue crosses the line and becomes a true cancer.

Random migration: In healthy tissues, the cells stay where they are, adhering to each other in structures that characterize the tissue and assist in its function. Mature cancer cells, in contrast, can let go of these molecular handholds, and relocate to other parts of the body. This cell movement, called metastasis, is one of the most defining characteristics of malignance. The resulting eruption of tumors in distant parts of the body is what brings about the majority of deaths from cancer.

Taken together, these rogue qualities are considered the hallmarks of cancer. Precancerous cells may show uncontrolled growth and lack appropriate response to stop signals and so they may divide repeatedly. Each new division is subject to frequent genetic errors. When such cells proliferate, they continue to pass along their disruptive mutations and likely acquire new ones, eventually creating a cancerous tumor. Tumor cells often acquire the first five characteristics before they move out to other parts of the body. This helps explain why catching a cancer early is important: If you detect it before it has acquired all the hallmarks, you can prevent metastasis.
 
One of the hallmarks of a cancer cell is aggressive, disorderly growth. Compare the slower-growing field of normal cells in the first movie to the messier field of cells in the second movie.