Cancer is a group related diseases. In all types of cancer, some of the body's cells begin to divide without stopping and spread into surrounding tissues.
Normally, new cells form as you need them, replacing old cells that die. Sometimes, this process goes wrong. New cells form when you don't need them, and old cells don't die when they should. The extra cells can form a tumor. Tumors can be benign or malignant. Benign tumorsaren't cancer while malignant ones are. Cells from malignant tumors can invade nearby tissues. They can also break away and spread to other parts of the body.
Children can get cancer in the same parts of the body as adults, but there are differences. Childhood cancers can occur suddenly, without early symptoms, and have a high rate of cure. The most common children's cancer is leukemia. Other cancers that affect children include brain tumors, lymphoma, and soft tissue sarcoma.
Symptoms and treatment depend on the cancer type and how advanced it is. Treatments include surgery, radiation therapy, chemotherapy, stem cell transplants, and/or targeted therapy. Targeted therapy uses substances that attack cancer cells without harming normal cells.
NIH: National Cancer Institute