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Understanding Cancer

Cancer is a disease of abnormal cell growth. Usually, the cells of our body grow and divide in a controlled way. When normal cells become damaged or old, they die and are replaced by healthy cells. In cancer, the signals that control cell growth don’t work properly. Cancer cells keep growing and multiplying when they should stop. In other words, cancer cells don’t follow the rules of healthy cells.

Microscope image that shows normal bone marrow

This microscope image shows normal, healthy bone marrow.

Microscope image shows bone marrow of a patient with acute lymphoblastic leukemia

This microscope image shows the bone marrow of a patient with acute lymphoblastic leukemia.

Every cell is controlled by genes that provide instructions that tell cells how to function and when to grow and divide. Cancer develops from the body’s own cells: it begins with a change within the genes of a single cell. Genetic changes, or mutations, can interfere with the normal function of a cell. Most mutations are harmless, but sometimes these mutations disrupt the control of cell growth. Only rarely are these gene changes inherited from parents. Most of the time the mutations arise spontaneously as mistakes when cells divide. Unlike some adult cancers, pediatric cancers are not likely to be caused by lifestyle or environmental factors. Rather, childhood cancers mostly arise due to gene mutations that happen by chance.

Cancer is usually named for the type of cell or tissue where it starts. Over 100 different types of cancers occur in children. How cells look under the microscope and the molecular and genetic features of the cells give information to help determine the specific type of cancer.

Every cell is controlled by genes that tell cells how to function and when to grow and divide.

Every cell is controlled by genes that tell cells how to function and when to grow and divide.

Many cancers form masses, or clumps of cells, that make up a solid tumor. Other cancers, like leukemia, circulate in the blood and do not form masses. As solid tumors grow, some cells may travel to other parts of the body. This process is called metastasis. Cancer may also directly spread to nearby tissue, a process called invasion. The original place where cancer starts is called the primary tumor. Metastatic cancer is named for the original tumor. For example, osteosarcoma that starts in bone but can spread to the lung, where it is called metastatic osteosarcoma, not lung cancer.

Cancer cells often have characteristics that increase their chance to grow. The cells may divide more quickly than normal cells or simply not stop dividing when they’re supposed to. Some cancer cells continue to develop new gene mutations that can cause them to multiply faster. As cancer cells grow and invade healthy tissue, tumors can press on blood vessels, nerves, and important structures to keep body systems from working properly. The cancer cells can crowd out healthy cells and interfere with normal functions.

The main treatments for pediatric cancer include surgery, chemotherapy, radiation therapy, immunotherapy, and targeted therapy. The type and combination of treatments used for cancer depends on many factors. These include:

  • The type of cancer including gene mutations
  • Where the tumor is located
  • Whether the cancer is new or has come back
  • The stage of cancer including the size of tumor and whether the cancer has spread to other parts of the body
  • The age of the child

For many types of childhood cancer, improving therapies have increased survival rates, which overall now average 80% or higher in the United States. However, for other cancers, the prognosis remains poor. Scientists are learning more about the genetic causes of cancer and specific features of cancer cells. These discoveries will continue to improve the diagnosis and treatment of pediatric cancer.

Reviewed: June 2018