Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma occurring in children. Disease onset is observed at 2–5 years of age, with a significant rise in morbidity in adolescents > 12 years.
The name, RMS, is derived from the histological origin of the cells observed under a microscope ─ rhabdomyoblasts, which are primitive muscle cells. This tumor can occur anywhere in the body; however, a primary bone rhabdomyosarcoma has not been reported. The most common sites are the head and neck (about 40%), and include parameningeal tumors (nasal cavity, nasopharynx, paranasal sinuses, middle ear and skull base), orbital and neck tissues including salivary glands, oral cavity, larynx, middle and lower pharynx, thyroid gland and cheek RMS. RMS is also found in the extremities, genitourinary tract, trunk and in the retroperitoneum.
The histologic forms manifest with following variations: the embryonal rhabdomyosarcoma (55% of patients), botryoid variant of ERMS (5% of patients), alveolar rhabdomyosarcoma( 20% of patients), and the undifferentiated sarcoma (20% of patients). Treatment and prognosis depends on these different presentations.
Symptoms usually occur late and the disease may have already metastasized to lungs and liver, by the time the RMS is diagnosed. Orbital tumors, however, carry a favorable prognosis as exophthalmos occurs early providing an early diagnosis and treatment. Other favorable localizations include each site in the head and neck that is not in the parameningeal region, as well as genitourinary organs (excluding urinary bladder and prostate) and bile duct.
Prognosis and treatment depends on histology and staging of the RMS. Morbidity and mortality in RMS has significantly improved over the past few decades with great strides being made in diagnosis and treatments available today.
A multidisciplinary team is involved in treating and providing therapeutic protocols. Immunology and genetics are guiding new therapeutic modalities in oncology. Molecular testing can help not only in diagnosing but also in monitoring the minimal residual disease.
The management of Rhabdomysarcoma includes a biopsy followed by staging using either a CT/MRI or PET-CT scan. The first line of treatment is chemotherapy for 4 cycles followed by a local treatment either surgery or radiation ,if the tumour is non operable. Sometimes in parameningeal RMS radiation is given alone and in some cases after surgery. This is followed by 8-11 courses of further chemotherapy depending upon the response to first set of chemotherapy,complete removal at surgery or complete disappearance after radiation.
Modern aggressive chemotherapy includes vincristine, cyclophosphamide, actinomycin D, doxorubicin, isophosphamide, and etoposide. Advanced surgical techniques in skull base surgery, microsurgery and reconstruction surgery have led to extension of survival rates in RMS.
Radiation therapy, apart from surgery is an important method for local tumor control. Delaying radiotherapy has been associated with increased risk of local tumor relapse. Usually, surgery and radiation therapy are considered at the earlier stages of treatment. Radiation dosage can be reduced to smaller amounts in patients after microscopically incomplete surgical resection, while residual tumors and initially un-resected tumors require higher doses.
The real challenges for the radio-oncologists are treating children under the age of 3, in whom the risk of adverse events secondary to radiotherapy is significantly greater. In order to increase the safety of radiation therapy, conformal radiotherapy, intensity-modulated radiation therapy (IMRT) and proton therapy have been used.
The efficacy of brachytherapy in the treatment of sarcomas is very encouraging. Radiationhas also been applied directly to the tumor and is associated with fewer complications in comparison with conventional radiotherapy. High effectiveness of that method has been proved in the treatment of RMS of the genitourinary tract and extremities. Research is ongoing to further improve prognosis in advanced RMS.
RMS is one of the childhood cancers where appropriate use of all modalities has given very high success rates with organ preservation and good quality of life for children.