Rhabdomyosarcoma

A rhabdomyosarcoma is a type of cancer, specifically a sarcoma (cancer of connective tissues), in which the cancer cells are thought to arise from skeletal muscle progenitors. It can also be found attached to muscle tissue, wrapped around intestines, or in any anatomic location. Most occur in areas naturally lacking in skeletal muscle, such as the head, neck, and genitourinary tract.

Presentation
Its two most common forms are embryonal rhabdomyosarcoma and alveolar rhabdomyosarcoma. In the former, which is more common in younger children, the cancer cells resemble those of a typical 6-to-8-week embryo. In the latter, which is more common in older children and teenagers, they resemble those of a typical 10-to-12-week embryo.

Epidemiology
Rhabdomyosarcoma is a relatively rare form of cancer.

It is most common in children ages one to five, and is also found in teens aged 15 to 19, although this is more rare. This cancer is also an adult cancer but it is rare.

St. Jude Children's Research Hospital reports that rhabdomyosarcoma is the most common soft tissue sarcoma in children. Soft tissue sarcomas make up about 3% of childhood cancers.

Diagnosis
The diagnosis of rhabdomyosarcoma is made by a pathologist, a physician who specializes in the diagnosis of disease. The pathologist will examine a biopsy of the tumor under the microscope and arrive at the diagnosis of rhabdomyosarcoma based on the morphology (appearance) of the tumor cells and the results of immunohistochemical stains.

Diagnosis of rhabdomyosarcoma depends on recognition of differentiation toward skeletal muscle cells. The proteins myoD1 and myogenin are transcription factor proteins normally found in developing skeletal muscle cells which disappears after the muscle matures and becomes innervated by a nerve. Thus, myoD1 and myogenin are not usually found in normal skeletal muscle and serve as a useful immunohistochemical marker of rhabdomyosarcoma.

Early manifestation can be misdiagnosed as a pseudotumor that is non responsive to steroid treatment.

Classification
Several different histological subtypes of rhabdomyosarcoma exist, each of which has different clinical and pathological characteristics. Prognosis and clinical behavior of the tumor is also partially dependent on histologic subtype. Multiple classification systems have been proposed for subclassifying these tumors. The most recent classification system, the "International Classification of Rhabdomyosarcoma", was created by the Intergroup Rhabdomyosarcoma Study. This system attempts to combined elements of the previous systems and correlate these with prognosis based on tumor type.

International Classification of Rhabdomyosarcoma

Several additional subtypes of rhabdomyosarcoma exist that do not fit into the International Classification scheme. Pleomorphic rhabdomyosarcoma usually occurs in adults rather than children, and, thus, is not included in this system. Sclerosing rhabdomyosarcoma is a rare rhabdomyosarcoma subtype recently characterized by Folpe, et al; it is not included in this system.

Although botryoid and spindle cell rhabdomyosarcoma are classically considered as subtypes of embryonal rhabdomyosarcoma, they have more favorable clinical behavior and prognosis than classic embryonal rhabdomyosarcoma.

Treatment
Treatment for rhabdomyosarcoma consists of chemotherapy, radiation therapy and sometimes surgery. Surgery to remove the tumor may be difficult or impossible depending on the location of the tumor.

If there is no evidence of metastasis, surgery combined with chemotherapy and radiation offers the best prognosis. Patients whose tumors have not metastasized usually have a good chance for long-term survival, depending on the subtype of the tumor.

St Jude's Children's Research Hospital reports that more than 70% of children diagnosed with localized rhabdomyosarcoma have long-term survival.

Tungsten Alloy and RMS
A study has shown a link between RMS and Tungsten alloy embedded in muscle (e.g. shrapnel). However, the tungsten alloy contained 6% Nickel and 3% Cobalt, which are known carcinogens. A synergistic effect of alloying tungsten with Ni and Co is suggested (i.e. increasing the toxicity relative to either of the pure metals).