First, it’s important to understand what cancer is. Cancer is the result of mutations in an organism’s DNA that cause a cell to start growing much faster than other cells, so it out competes other cells. A lot of times the mutation is in a gene that is important for stopping mutations so the cell soon gathers many mutations. So this mutated cell keeps dividing leaving many “children” cells that are less useful to the body than the cells that are starving from being out competed. Eventually this develops into a huge cluster of cells called a tumor and since these cells like to grow, they will spread to other parts of the body and grow there. Eventually they make it into the “body’s police headquarters” called the lymph node and sometimes the brain.

Mutations in DNA are natural and unavoidable. They occur due to errors in making copies of DNA and due to external things like UV sunlight and cigarette smoke. Therefore even if you lived in a bubble, you would eventually get cancer, though you get it faster if you do things like smoke. In addition, some people are more likely to get certain cancers based on their DNA in that is easier for a part of their DNA to mutate to a bad form. While DNA mutations can be very bad in the case of cancer, they are also one of the driving force behind evolution. For instance, it was DNA mutations that led to humans getting progressively larger brains so that we can wonder what caused cancer in the first place. Most mutations however are neutral and don’t help or hurt the cell. Therefore cancer has to exist because DNA mutations will happen eventually, though it is possible to reduce this rate. A typical DNA replication will only make 3 mistakes in the DNA code of 3 billion letters so cancer is still rare. To get rid of cancer, we would either need to make sure the DNA had fewer mistakes which would take extensive human genetic engineering or more likely get rid of the early cancer cells before they will be a problem. So you couldn’t really get rid of cancer forever, though you could design a treatment that always kills the cancerous cells early so that nobody ever dies from cancer.

Cancer is caused by a mutation in the DNA of cells that breaks the cells' ability to stop multiplying. They then multiply out of control. Anything capable of causing mutations - be it high-energy light, radioactive materials, or toxic chemicals that affect DNA (some of which are necessary for life) can cause cancer.

There is no way to get rid of cancer forever, because there is no way to stop mutations. There may be better ways to treat it, though, to turn it from something deadly to something merely annoying like the common cold.

There are many things that can cause or increase the risk of different types of cancer. For example, carcinogens (cancer-causing substances or exposures) can include things like cigarette smoke, radon gas, UV light, many laboratory chemicals and chemicals in gasoline, cleaning products, even naturally occurring chemicals in some foods.

Although many things are classified as carcinogens, it doesn't mean that they cause cancer in all people, or in any dose, or at any age. Cancer occurs most frequently in older people because the genetic integrity of human cells degrades as people accumulate carcinogenic damage to their cells throughout their lifetimes.

Lifestyle choices can reduce the chances of getting cancer at a young age, including maintaining a healthy body weight, eating ample amounts of fruits and vegetables. Even with healthy lifestyle, however, sometimes cancer can strike, and this can be very difficult to deal with, especially if ourselves or a loved one is affected. This is especially true if the person is young.

You asked why cancer has to exist. Well, cancer doesn't exactly HAVE to exist in the world, except that our cells and our bodies just aren't that permanent, and they accumulate damage over time that is inevitable. If something else doesn't kill us first, eventually cancer is often the thing that does.

The bright side of the story is that these days, people are living long enough for cancer to be a major cause of death as opposed to facing deaths by the many illnesses that used to kill people at much younger ages. Additionally, many cancers are treatable if caught in time.

You asked if there is a way to get rid of cancer forever. I don't think so any time soon. It's almost like solving the problem of living forever. I do, however, think that the age at which the average person dies from cancer will steadily increase as medical detection and treatments continue to improve.

If you are experiencing cancer in your family now, I wish the best for you. My Mom had cancer, which was luckily caught early and was treatable, and she recovered. It reminded me, though, that you never know when you might lose somebody, so it's important to be good to the people who love you and tell them often that you love them back.

Our cells normally divide in a controlled way to renew and replace tissue. Cancer is essentially uncontrolled cell division. We are still learning about the causes of cancer and it is apparent that many factors can lead to cancer onset and progression. For example, radiation (for example from the sun) can cause cancer as it produces free-radicals in our cells that can change DNA sequences. If free radicals change the DNA sequence in a gene that controls cell division, this can lead to cancer. Cancer exists because the mechanisms our cells use to divide are not perfect and are sensitive to our environment. Some creatures seem especially resistant to developing cancer, and scientists are studying these animals to understand how cancer may be avoided. Although there is currently not a way to assure that no one will ever get cancer, scientists are hopeful that current research will lead to successful ways to prevent and treat cancer.