Do we know what causes rhabdomyosarcoma?
Researchers do not know what causes most cases of rhabdomyosarcoma (RMS), but they are learning how normal cells become cancerous because of certain changes in their DNA. DNA is the chemical in each of our cells that makes up our genes – the instructions for how our cells function. It is packaged in chromosomes (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 control when our cells grow, divide into new cells, and die. Genes that help cells grow, divide, or stay alive are called oncogenes. Others that slow down cell division or make cells die at the right time are called tumor suppressor genes. Cancers can be caused by DNA changes that turn on oncogenes or turn off tumor suppressor genes.
For example, people with Li-Fraumeni syndrome have changes in the TP53 tumor suppressor gene that cause it to make a defective p53 protein. The p53 protein normally causes cells with DNA damage to either pause and repair that damage or, if repair is not possible, to self-destruct. When p53 is not working, cells with DNA damage keep dividing, which can lead to further defects in other genes that control cell growth and development. This can lead to cancer.
Certain genes in a cell can be turned on when bits of DNA are switched from one chromosome to another. This type of change, called a translocation, can happen when a cell is dividing into 2 new cells. This seems to be the cause of most cases of alveolar rhabdomyosarcoma (ARMS). In these cancers, a small piece of chromosome 2 (or, less often, chromosome 1) ends up on chromosome 13. This moves a gene called PAX3 (or PAX7 if it’s chromosome 1) right next to a gene called FOXO1. The PAX genes play an important role in cell growth while an embryo’s muscle tissue is being formed, but these genes usually shut down once they’re no longer needed. The normal function of the FOXO1 gene is to activate other genes. Moving them together probably activates the PAX genes, which may be what leads to the tumor forming.
Research suggests that embryonal rhabdomyosarcoma (ERMS) develops in a different way. Cells of this tumor have lost a small piece of chromosome 11 that came from the mother, and it has been replaced by a second copy of that part of the chromosome from the father. This seems to make the IGF2 gene on chromosome 11 overactive. The IGF2 gene codes for a protein that can make these tumor cells grow. Other gene changes are probably important in these tumors as well.
Changes in several different genes are usually needed for normal cells to become cancer cells. Scientists have found some other gene changes that set some RMS cells apart from normal cells, but there are likely still others that haven’t been found yet.
Researchers now understand many of the gene changes that can lead to RMS, but it’s still not clear what causes these changes. Some gene changes can be inherited. Others might just be a random event that sometimes happens inside a cell, without having an outside cause. There are no known lifestyle-related or environmental causes of RMS, so it’s important to know that there is nothing children with RMS or their parents could have done to prevent these cancers.
Last Medical Review: 11/20/2014
Last Revised: 11/21/2014