Cancer
Although childhood cancer is rare, approximately 13,000 children under the age of 20 are diagnosed with cancer every year. Cancer affects people regardless of age, sex, race, geographical location or social status. Oncology, the study of cancer and tumors, has made significant progress in the prevention, treatment, and prognosis of many childhood cancers. Despite this progress, cancer is the third most common cause of death in children ages 1 to 19.
Childhood cancer varies from adult cancers in development, treatment, response to therapy, tolerance of therapy, and prognosis. The future direction of oncology involves genetic research and improved treatment options. Discovery of certain "cancer genes" has made significant breakthroughs in the study of cancer. Much more investigation into human genes and development are still needed to understand cancer.
What is cancer?
Cancer is an abnormal growth of cells. Cancer cells rapidly reproduce despite restriction of space, nutrients shared by other cells, or signals sent from the body to stop reproduction. Cancer cells are often shaped differently than healthy cells, they do not function properly, and they can spread to many areas of the body.
The number of cells in each body tissue is tightly controlled. The number of new cells made equals the number needed to replace dying cells plus the number needed for growth and development. Unlike normal cells, tumors are clusters of cells that are capable of growing and dividing uncontrollably. Their growth is not regulated.
Tumors can be benign (non-cancerous), or malignant (cancerous). Benign tumors tend to grow slowly and do not spread. Malignant tumors grow rapidly, can invade and destroy nearby normal tissues, and can spread throughout the body. The term "cancer" is used when a tumor is malignant.
Cancer is malignant because it can be "locally invasive" and "metastatic":
- Locally invasive: the tumor can invade the tissues surrounding it by sending out 'fingers' of cancerous cells into the normal tissue.
- Metastatic: the tumor can send cells into other tissues in the body, which may be distant from the original tumor.
The original tumor is called the "primary tumor." These cells which travel through the body can begin the formation of new tumors in other organs. These tumors are referred to as "secondary tumors." The cancerous cells travel through the blood (circulatory system) or lymphatic system to form secondary tumors.
The lymphatic system is a series of small vessels that collect waste from cells, carrying it into larger vessels, and finally into lymph nodes. Lymph fluid eventually drains into the bloodstream. When cancer spreads, it is still named after the part of the body where it started. For example, if kidney cancer spreads to the lungs, it is still kidney cancer, not lung cancer. (The lung cancer would be an example of a secondary tumor.)
"Staging" is the process of finding out whether cancer has spread and if so, how far. There is more than one system used for staging. Cancer is not just one disease but rather a group of diseases. All forms of cancer cause cells in the body to change and grow out of control.