Sarcomas are cancers that develop from connective tissues in the body, such as muscles, fat, membranes that line the joints, or blood vessels. There are many types of sarcomas. Rhabdomyosarcoma is a cancer made up of cells that normally develop into skeletal muscles. The body contains 3 main types of muscles.
- Skeletal (voluntary) muscles are muscles that we control to move parts of our body.
- Cardiac muscle is the main muscle type in the heart.
- Smooth muscle is the main type of muscle in internal organs (except for the heart). For example, smooth muscles in the intestines push food along as it is digested. We do not control this movement.
About 7 weeks into the development of an embryo, rhabdomyoblasts (cells that will eventually form skeletal muscles) begin to form. These are the cells that can develop into the cancer called rhabdomyosarcoma. Because this is a cancer of embryonal cells, it is much more common in children, although it does occur in adults occasionally.
We think of our skeletal muscles as being mainly in our arms and legs, but these skeletal muscle cancers can start nearly anywhere in the body. Common sites include:
- Head and neck (near the eye, inside the nasal sinuses or throat, or near the spine in the neck)
- Urinary and reproductive organs (bladder, prostate gland, or any of the female organs)
- Arms and legs
- Trunk (chest and abdomen)
Rhabdomyosarcomas can even start in some parts of the body that don't normally have skeletal muscle.
Types of rhabdomyosarcoma
There are 2 main types of rhabdomyosarcomas.
Embryonal rhabdomyosarcoma
Embryonal rhabdomyosarcoma (ERMS) is the most common type of rhabdomyosarcoma. It usually affects infants and young children. The cells of ERMS look like the developing muscle cells of a 6- to 8-week-old embryo. ERMS tends to occur in the head and neck area, bladder, vagina, and in or around the prostate and testicles.
Two subtypes of ERMS, botryoid and spindle cell rhabdomyosarcomas, tend to have a better prognosis (outlook) than the more common forms.
Alveolar rhabdomyosarcoma
Alveolar rhabdomyosarcoma (ARMS) typically affects older children or teenagers and occurs more often in large muscles of the trunk, arms, and legs. ARMS cells look like the normal muscle cells seen in a 10-week-old fetus. ARMS tends to grow faster than ERMS and usually requires more intensive treatment.
Anaplastic rhabdomyosarcoma and undifferentiated sarcoma
Anaplastic rhabdomyosarcoma (formerly called pleomorphic rhabdomyosarcoma) is an uncommon type that occurs in adults but is very rare in children.
Some doctors also group undifferentiated sarcomas with the rhabdomyosarcomas. Doctors can tell that these cancers are sarcomas using lab tests, but the cells don't have any features that help classify them further.
Both of these uncommon cancers tend to grow quickly and usually require intensive treatment.
Rhabdomyosarcoma in adults
Most rhabdomyosarcomas occur in children, but they can also occur in adults. Adults are more likely to have faster-growing types of rhabdomyosarcoma, to have them in parts of the body that are harder to treat, and to have them spread to other parts of the body at the time of diagnosis. This is why, rhabdomyosarcomas in adults are often harder to treat effectively.
This document focuses on rhabdomyosarcomas in children, but most of the information here (including much of the treatment information) applies to rhabdomyosarcomas in adults as well.
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