Literature review

Literature review

Cancer

Cancer isn't just a single condition; it's actually a complex collection of diseases that can arise in almost any tissue in the body. What characterizes full-blown cancer cells is that they've become decidedly anti-social, carrying on their activities without re- gard to the other cells and tissues around them. Most normal cells are monitored by a myriad of mechanisms that keep them working in cooperation with other cells. When damage prevents them from doing so, they ?x themselves or die. Every cancer starts as a disruption of this normal activity. For example, most cells know it's time to divide when they get signals from nearby cells or other parts of the body. Cancer cells, however, will divide whenever they please, regardless of how much they crowd their neighbors. They'll also move to places they don't belong, attract blood vessels to themselves, and stop obeying aging signals. In short, cancer cells misbehave, and their mischief gives rise to tumors.

Each cancer has its own unique pattern of bad behavior determined by the tissue in which it was formed, the mutations the cells have adopted, and the chemistry in an individual's body. Because every cancer is unique, a treatment that works wonders for a leukemia patient, for example, might do little or nothing for a woman with breast cancer. Even patients who have the same kind of cancer will have di?erent responses to the same therapy, because the way the cancer arises and plays out depends on unique cellular events and the patient's individual genome.

Pro?le of a cancer cell

Even though every cancer is di?erent, there's a shared set of behaviors that character-izes 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 in?nitely:

Healthy cells eventually stop dividing but continue to live. Their growth is stopped by the fact that ...