What is cancer?

Cancer is an abnormal growth of cells. The whole body is made of cells that act and grow in controlled ways as the body needs them. The cells are controlled by genes. The genes in any 1 of these cells can become damaged. Then the cell can grow out of control and become cancer.

Cancer cells quickly grow and divide. This happens even when there's not enough space and nutrients. They also grow despite signals sent from the body telling them to stop.

Cancer cells don't look the same as healthy cells. They don't work the way they should. They can spread to other parts of the body. Tumors, masses, or lesions are names for abnormal growths of cells that can become cancer. Oncology is the branch of medicine that studies and treats cancer.

What do benign and malignant mean?

Tumors can be benign or malignant.

  • Benign tumors are not cancer. They tend to grow slowly. They do not spread to other parts of the body.
  • Malignant tumors are cancer. They can grow quickly. They grow into and destroy nearby normal tissues. And they can spread throughout the body.

What do locally invasive and metastatic mean?

Cancer can be locally invasive and metastatic.

  • Locally invasive cancer has spread to nearby tissues. It can cause problems by pressing on nearby tissues and organs. This can make them unable to work the way they should.
  • Metastatic cancer has spread from where it first started. It is growing in and affecting another part of the body. Cancer cells spread by getting into your blood stream or lymph system. The lymph system is a series of small vessels that carry a fluid called lymph. Lymph collects waste from cells. It carries it into lymph nodes where the waste is filtered out. Lymph then drains into your bloodstream.

Cancer cells can travel through 1 of these pathways to any part of the body. Then they grow and form a tumor there.

What are primary tumors?

  • The original tumor is called the primary tumor. This is the place where the cancer first started. These cells can break off and travel through the body. Then they can start to form new tumors in other organs.
  • These new tumors are called secondary tumors. The cancer cells travel through your blood or lymph system to form these tumors.

How is each cancer type named?

Cancer is named after the part of the body where it first started. This is the place the original tumor formed.

When cancer spreads, it keeps this same name. For example, if kidney cancer spreads to your lungs, it’s still called kidney cancer. The cancer in the lung is a secondary tumor. The cancer cells in the lung look like the cancer cells in the kidney. They don't look like lung cancer cells. This may be called kidney cancer with lung metastasis or metastatic kidney cancer to the lung. It's not called lung cancer.

What are the different types of cancer?

Cancer is not just 1 disease. It’s a group of many diseases, all of which cause cells in the body to change and grow out of control. Cancers are defined by the kind of cell they start in. Or they can be defined by the place in the body where they first started. Some cancers are of mixed types. These are the most common categories of cancer:

  • Carcinoma. This is cancer found in cells that make up epithelial tissue. This tissue covers or lines the surfaces of organs, glands, and body structures. Carcinoma usually forms a solid tumor. Carcinomas are 80% to 90% of all cancers.
  • Sarcoma. This is cancer that starts in connective tissue cells. These can include blood and lymph vessel, cartilage, fat, muscle, tendon, and bone cells. For example, osteosarcoma is the most common type of cancer that starts in the bone. Chondrosarcoma is cancer that starts in cartilage cells.
  • Lymphoma. This is cancer that starts in a type of white blood cell called a lymphocyte. These cells are part of the immune system, Lymphoma cells can build up in lymph nodes and other lymph tissues. Lymphomas are grouped into 2 categories: Hodgkin lymphoma and non-Hodgkin lymphoma.
  • Leukemia. This is called a blood cancer. It starts in the cells in the bone marrow that make blood cells. This type of cancer keeps the marrow from making normal red and white blood cells and platelets. White blood cells are needed to fight infections. Red blood cells are needed to carry oxygen and carbon dioxide through the body. Platelets keep the body from bruising and bleeding easily. There are 4 main types of leukemia. They are acute myelogenous leukemia (AML), chronic myelogenous leukemia (CML), acute lymphocytic leukemia (ALL), and chronic lymphocytic leukemia (CLL). The terms myelogenous and lymphocytic mean the type of cells that are involved. Acute and chronic tell how fast the cells are growing.
  • Myeloma. This type of cancer starts in the plasma cells of bone marrow. In some cases, the myeloma cells collect in 1 bone and form a single tumor. This is called a plasmacytoma. In other cases, the myeloma cells collect in many bones. It forms many tumors. This is called multiple myeloma.

What causes cancer?

Cancer has no single cause. Experts think that it’s the interaction of many factors that leads to cancer. The factors may be genetic, environmental, or lifestyle. These factors cause a change in the genes of a cell so that it divides and grows in an uncontrolled way.

Who is at risk for cancer?

Some cancers have been linked with risk factors. A risk factor is anything that may increase your chance of getting a disease. A risk factor doesn't necessarily cause the disease. But it may mean you’re more likely to get it. People with an increased risk of some cancers can help reduce their risk by getting regular screening tests. This allows pre-cancer cells to be found and treated before they turn into cancer cells. Some colon, rectal, and cervical cancers can be prevented with screening.

Reducing certain risk factors can also help. Cancer treatment tends to work better when the cancer is found early. This means when it's small and hasn't spread. Some known risk factors for cancer in adults include:

  • Lifestyle factors. These include smoking, a high-fat diet, and exposure to ultraviolet light (UV) from the sun or UV lamps. These are only risk factors for adult cancers. Most children with cancer are too young to have been exposed to lifestyle factors long enough to have them cause cancer.
  • Genetic factors. Family health history and genes play a role in some cancers. Some cancers run in families. Some gene changes are inherited. This means people in these families have a higher risk for some types of cancers. But not every family will get cancer. In many cases, it isn’t known if the disease is caused by a gene change, other factors, or a coincidence.
  • Virus exposure. Contact with certain viruses have been linked to cancer. These include the human papillomavirus (HPV) and HIV, the virus that causes AIDS. These viruses can cause cells changes that may lead to cancer over time. But cancer isn’t contagious. You can't get it from contact with another person.
  • Environmental factors. People with certain jobs seem to have a higher risk of some cancers. This includes painters, farmers, construction workers, and people in the chemical industry. This is likely due to contact with certain chemicals. Some environmental factors in your home may be linked to cancer. These can include a natural radioactive gas called radon, and arsenic in well water.

How do genes affect cancer growth?

Certain genes contribute to cancer. All cancers have some type of genetic change (mutation). A small amount of these mutations are inherited. But the rest happen by chance.

There are 3 main types of genes that can affect cell growth. They are changed (mutated) in certain types of cancers. These include:

  • Oncogenes. These genes control the normal growth of cells. Scientists say oncogenes are like a cancer "switch" that most people have in their bodies. It isn’t known what "flips the switch" to take away control and allow abnormal cancer cells grow.
  • Tumor suppressor genes. These genes are able to spot abnormal growth and reproduction of damaged cells, like cancer cells. They can stop them from reproducing. But if the tumor suppressor genes are mutated and don’t work well, cancer cells can grow.
  • Mismatch-repair genes. These genes help find errors when the DNA in genes is copied to make a new cell. If the DNA does not "match" perfectly, these genes repair the mismatch and correct the error. But if these genes aren’t working well, errors in DNA can transferred to the new cells. This causes them to be damaged.

In most cases, the number of cells in our body tissues is tightly controlled. New cells are made for normal growth and development. They're also made to replace damaged or dead cells. Cancer is a loss of this balance. It starts when genetic changes "tip the balance" in favor of excessive cell growth.

How do childhood and adult cancers differ?

Diagnosis, treatment, and prognosis for childhood cancers are different than for adult cancers. The main differences are the survival rate and the cause of the cancer.

The 5-year survival rate for childhood cancer is about 83%. This means that 83 out of 100 children with cancer will survive 5 years. The 5-year survival rate for adult cancers is about 67%. This may be because childhood cancer responds better to certain treatments. Unlike adults, children don't usually have other health problems that can affect cancer treatment.

A cell change that occurs by chance is the most common cause of most childhood cancers. In adults, lifestyle and environmental risk factors are strongly linked to cancer. Adult cancers are sometimes called acquired for this reason.

Another key difference is clinical trials. Most children are treated at special childhood cancer centers and most are treated in clinical trials. This means they're treated by experts. They get the very best available, cutting-edge treatments that help improve childhood cancer treatment at a rapid rate. Fewer than 1 in 20 adults takes part in cancer clinical trials. This affects the development of new procedures and treatments.