What Is Cancer?

Cancer is the name for a group 100+ diseases that affect different parts of the body. Although there are many kinds of cancer, all cancers start because abnormal cells grow out of control. Untreated cancers have the ability to cause serious illness and death.

How Cancer Starts

The body is made up of trillions of living cells. Normal body cells grow, divide, and die in an orderly fashion. During the early years of a person’s life, normal cells divide faster to allow the person to grow. After the person becomes an adult, most cells divide only to replace worn-out or dying cells, or possibly to repair injuries.

Cancer starts when cells in a part of the body start to grow out of control. Cancer cell growth is different from normal cell growth. Instead of dying, cancer cells continue to grow and form new, abnormal cells. Cancer cells can also invade (grow into) other tissues, something that normal cells cannot do. Growing out of control and invading other tissues are what makes a cell a cancer cell.

Cells become cancer cells because of DNA (deoxyribonucleic acid) damage. DNA is in every cell and it directs all the cell’s actions. In a normal cell, when DNA gets damaged the cell either repairs the damage or the cell dies. In cancer cells, the damaged DNA is not repaired, and the cell doesn’t die like it should. Instead, the cell goes on making new cells that the body doesn’t need. These new cells all have the same abnormal DNA as the first cell does.

People can inherit abnormal DNA, but most DNA damage is caused by mistakes that happen while the normal cell is reproducing, or by something in the environment. Sometimes the cause of the DNA damage may be something obvious like cigarette smoking or sun exposure. But it’s difficult to know exactly what caused any one person’s cancer.

In most cases, the cancer cells form a tumor. Some cancers, like leukemia, rarely form tumors. Instead, these cancer cells involve the blood and blood-forming organs and circulate through other tissues where they grow.

How Cancer Spreads

Cancer cells often travel to other parts of the body where they begin to grow and form new tumors. This happens when the cancer cells get into the body’s bloodstream or lymph vessels. Over time, the tumors replace normal tissue. The process of cancer spreading is called metastasis.

How Cancers Differ

No matter where a cancer may spread, it’s always named for the place where it started. For example, breast cancer that has spread to the liver is called metastatic breast cancer, not liver cancer. Likewise, prostate cancer that has spread to the bone is called metastatic prostate cancer, not bone cancer.

Different types of cancer can behave very differently. For instance, lung cancer and skin cancer are very different diseases. They grow at different rates and respond to different treatments. This is why people with cancer need treatment that is aimed at their kind of cancer.

Tumors That Are Not Cancer

Not all tumors are cancer. Tumors that aren’t cancer are called benign. Benign tumors can cause problems – they can grow very large and press on healthy organs and tissues. But they cannot grow into (invade) other tissues. Because they can’t invade, they also can’t spread to other parts of the body (metastasize). These tumors are almost never life threatening.

How Common is Cancer?

Half of all men and one-third of all women in the US will develop cancer during their lifetimes.

Today, millions of people are living with cancer or have had cancer. The risk of developing many types of cancer can be reduced by changes in a person’s lifestyle, for example, by staying away from tobacco, limiting time in the sun, being physically active, and healthy eating.

There are also screening tests that can be done for some types of cancers so they can be found as early as possible – while they are small and before they have spread. In general, the earlier a cancer is found and treated, the better the chances are for living for many years

How Many New Cases Expected This Year?

About 1,660,290 new cancer cases are expected to be diagnosed in 2013. This estimate does not include carcinoma in situ (noninvasive cancer) of any site except urinary bladder, and does not include basal cell and squamous cell skin cancers, which are not required to be reported to cancer registries.

How Many People Are Expected to Die of Cancer This Year?

In 2013, about 580,350 Americans are expected to die of cancer, almost 1,600 people per day. Cancer is the second most common cause of death in the US, exceeded only by heart disease, accounting for nearly 1 of every 4 deaths.

What Percentage of People Survive Cancer?

The 5-year relative survival rate for all cancers diagnosed between 2002 and 2008 is 68%, up from 49% in 1975-1977 (see page 18). The improvement in survival reflects both progress in diagnosing certain cancers at an earlier stage and improvements in treatment. Survival statistics vary greatly by cancer type and stage at diagnosis. Relative survival compares survival among cancer patients to that of people not diagnosed with cancer who are of the same age, race, and sex. It represents the percentage of cancer patients who are alive after some designated time period (usually 5 years) relative to persons without cancer. It does not distinguish between patients who have been cured and those who have relapsed or are still in treatment. While 5-year relative survival is useful in monitoring progress in the early detection and treatment of cancer, it does not represent the proportion of people who are cured permanently, since cancer deaths can occur beyond 5 years after diagnosis.

Although relative survival for specific cancer types provides some indication about the average survival experience of cancer patients in a given population, it may or may not predict individual prognosis and should be interpreted with caution. First, 5-year relative survival rates for the most recent time period are based on patients who were diagnosed from 2002 to 2008 and thus, do not reflect the most recent advances in detection and treatment. Second, factors that influence survival, such as treatment protocols, other illnesses, and biological and behavioral differences of individual cancers or people, cannot be taken into account in the estimation of relative survival rates.

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