The cause of Ewing tumors is not fully understood, but researchers are learning how certain changes in a cell's DNA can cause the cell to become cancerous. DNA is the chemical in each of our cells that makes up our genes. Genes tell our cells how to function. They are packaged in chromosomes, which are long strands of DNA in each cell. We normally have 23 pairs of chromosomes in each cell (one set of chromosomes comes from each parent). We usually look like our parents because they are the source of our DNA. But DNA affects more than how we look.

Some genes contain instructions for controlling when our cells grow, divide, and die. Certain genes that speed up cell division are called oncogenes. Others that slow down cell division, or cause cells to die at the right time, are called tumor suppressor genes. Cancers can be caused by DNA mutations (changes) that turn on oncogenes or turn off tumor suppressor genes.

Researchers have found chromosome changes that lead to Ewing tumors, but these changes are not inherited. Instead, they develop in children after birth, in a single cell, for no apparent reason.

In about 85% of cases, the change is a swapping of genetic material between chromosomes 22 and 11. Less frequently, the swapping occurs between chromosomes 22 and 21, or rarely between 22 and another chromosome. This swapping is called a translocation. The result of this translocation is to move a certain piece of chromosome 11 (or another chromosome) just next to the EWS gene on chromosome 22, causing the EWS gene to be turned on all the time. The activation of the EWS gene leads to overgrowth of the cells and to the development of this cancer, although the exact way in which this happens is not yet clear.

Lab tests can be used to find chromosomal translocations in Ewing tumor cells (see "How are Ewing tumors diagnosed?"). If doctors are not sure if a tumor belongs to the Ewing family, they can use these tests to confirm the diagnosis.

Last Medical Review: 08/20/2009
Last Revised: 08/20/2009