The human body is a complex and wondrous living machine like any machine our bodies are composed of smaller parts that work together the various tasks that are performed each day such as breathing eating and digesting food and the movement of our blood are performed by specialized structures known as organs. Examples of organs include the lungs stomach, heart and brain. All of these organs and other body parts like our skin and muscles are made of smaller living units called cells. Our lungs are a good example of how many cells work together to perform a specialized task the cells in our lungs work together to allow us to take in oxygen from the air and get rid of waste products such as carbon dioxide. our lungs are composed of many millions of cells working together to accomplish this task cancer is the result of a long process that begins when one of the cells in an organ or tissue becomes damaged or altered in a way that causes it to break free from the normal controls that allowour cells to work together in harmony. A group of misbehaving cells can cause the same kinds of problems in a body that a defective part would cause in an yother type of machine. A normal cell will divide only when it receives a chemical signal telling it to do so these signals are interpreted in the nucleus and the cells reproduce their genetic information and divide into two identical daughter cells through a process called my mitosis.Cancer cells do not obey this rule and will divide even if they do no treceive appropriate signals in addition to the signals that normal cells receive telling them to divide they are also told when to stop dividing.This prevents too many cells from being made in fact the cell division process is a highly ordered process. This is acritical issue in cancer because cancer cells do notobey or require normal signals for division.This can lead to the formation of a mass of cells that piles up and may form a tumor. Alsodifferent from normal cells is the ability of cancer cells tocontinue dividing indefinitely An important point about cells is that no matter what their job is inthe body they all have the same general structure. the cells that make up our lungs, heart or brain are all similar in theiroverall appearance even though their jobs are quite different.just as the organs that the former made a smaller structures cells themselves are composed of smallerparts that help them perform their jobs. these smaller structures are calledorganelles. Of particular importance in cancer isthe organelle known as the nucleus.The nucleus can bethought of as the brains of a cell it contains the information that acts asthe blueprint for each and every one of us just as amanual would contain instructions to assemble a chair. Specifically this information iscontained within the chromosomes that reside in the nucleus. individual units have information arecalled genes. At a chemical level genes are made ofdeoxyribonucleic acid or DNA. All of our cells contain the sameset of information It is only how the information is usedthat makes them different. For example cells in the lungs usedifferent bits of the blueprint to do their job than the cells in our stomach.
In cancer changes to the DNA cause some of thegenes to fail to perform or to do their job in a way thatcauses problems for the affected individual In short all cancers are thought toresult from changes to DNA that alter critical genes and change thebehavior of the affected cells. If a change occurs to the nucleotidesequence it is like having the letters of a wordchanged. An alteration in a gene is called themutation How do all these changes occur?There are actually a number of different things that can cause mutations Examples include chemicals that can beswallowed or inhaled Such as those found in chewing tobaccoand cigarette smoke and radiation from the Sun or artificialsources like a tanning bedSometimes mutations occur without any known external causeThey just happen. Certain genes make productsthat lead cells to reproduce This would be equivalent to the gasolinesystem in cars The genes that are responsible formaking cells divide are known as Proto-Oncogenes.Changes in these normal genes lead to the production of OncogenesThe result may be cells that divide in the absence of proper signalsIt is the equivalent of a gas pedal that is stuck in the onposition Making a car go, even when no foot is pushing down. Genes whose products function as theequivalent of cellular breaks also exist As a group these genes are known as tumor suppressors Humans have two copies of each gene oneinherited from each parent If a single copy of a tumor suppressoris damaged the other copy is usually able to stop thecell from behaving abnormally This would be like losing either thefront or rear brakes of a car. The car may be damaged but would still be able to stop and butif the second set of brakes is damaged as well the car would not be able to stop.Just as the cell would not be able to stop dividing if both copies of the tumor suppressorgenes are damaged The process by which tumors cause thebody to provide them with nutrients is known as angiogenesisLike the hungry plant in the Little Shop of Horrors a growing tumors sends out signals thatessentially say feed meThe messages from the tumors cause nearby blood vessels to send over new extensions that deliverfood and oxygen Importantly, the blood vessels also serve as a passageway for themovement of tumor cells to neighboring and distant parts of the body. Spread of tumors to distant locations is of great importance in cancer. About ninety percent of the deaths dueto cancer involve tumors that have spread around the body.The movement of tumor cells to other parts of the body is known as metastasis.Metastasis is a complex process During which cancer cells break off theoriginal or primary tumor and move through thebody to form tumors at new locations From the point of view of a cancer cell,this is a dangerous and often unsuccessful processA trip through the body is full of hazards that cause the death of most cells that beginthe journey even tough cancer cells.To begin the process individual cells must break away fromthe tumor and invade nearby vessels the cells crawl along the surface ofother cells and the fibrous stringy structuressurrounding them and then force their way in.Shown here is the invasion of the blood supply.Once inside a blood vessel, the cancer cells may parish from avariety of causes Some cells die simply because they areunable to survive floating around in the bloodstream. Others may become damaged and die whenthey squeeze through tight spaces or bump into the walls of the blood vessels.Still other migrating cells may be recognizedand destroyed by cells of the immune system.How and where the migrating cells stop isdifferent for different cancer types Once the tumor cells are no longermoving they can begin the process of forming anew tumor by leaving the blood vessel andbeginning to reproduce in the new location This does not always occur and cells that have made it this far maystill die or fail to divide If the new environment is suitable thenewly-arrived cell will begin to grow and a new tumor will develop One way that the development of canceris prevented is via the death of defective cellsA cell that becomes mutated or damaged will first attempt to repair the damage.If that is not possible the cells will commit the cellularversion of suicide An orderly process called apoptosis leads to the breakdown of key cell partsand the death of the cell Cancer cells lose this criticalcapability and will continue to divideThis can lead to the accumulation of cells that can become more and more abnormal Due to the high rate at which cancercells accumulate mutations a tumor that originally started as asingle abnormal cell is actually made up of many slightlydifferent cells they are all cancer cells and aresimilar to each other but they may not all have the samesensitivity to any particular cancer drug or treatment When this mixed bag of cells is exposedto a drug, most to the cells will probably die. Those cancer cells that are resistant tothe treatment may reproduce to form a new tumorImportantly this new tumor will be unlikely torespond to the same treatment Their mutations make them invulnerableto that drug