Rhabdomyosarcoma (RMS) is a small round blue cell tumor more commonly seen in children and adolescents and only rarely in adults. There is limited data available regarding the management of RMS in adults. The treatment approaches for adult RMS have been extrapolated from the multimodality treatment guidelines for childhood RMS. In comparison, disease outcome is less favorable for adults than for children.
RMS is thought to arise from immature cells destined to form striated muscle, although tumors can arise in any part of the body, including in locations where skeletal muscle is not typically found.
The different subtypes include:
- Embryonal RMS
- Most common subtype, of intermediate prognosis
- Includes botryoid and spindle cell variants
- Alveolar RMS
- Defined by FOXO1 rearrangement by FISH or RT-PCR, with resultant fusion genes: PAX7-FOXO1 ;t(1;13) or PAX3-FOXO1; t(2;13) , found exclusively in alveolar RMS.
- Additional rare translocations have been described in alveolar RMS.
- This type of RMS has a relatively poorer prognosis
- Tumors usually present as a non-tender enlarging mass.
- Locations include head and neck (including orbital and parameningeal tumors), genitourinary tract, trunk and extremities.
- Regional lymph nodes involvement can be seen in RMS, unlike other soft tissue sarcomas.
- It is presumed that the majority of patients who present with apparently localized disease have subclinical metastases.
- Sites of metastases include lung, bone marrow, bone, omentum/ascites, and pleura. Visceral and brain metastases are rare.
Diagnostic and staging evaluation
- Biopsy should be performed at a facility with expertise in evaluation of bone and soft tissue sarcoma to ensure that the tissue is processed properly and to allow for the special studies needed for accurate diagnosis and histologic classification.
- Adequate tissue for routine light microscopy, immunohistochemistry, cytogenetic and molecular genetic studies should be obtained .
Imaging the primary site:
- Plain radiograph
- CT and or MRI
- In certain sites such as head and neck, extremity and pelvic tumors, MRI is preferred for its ability to attenuate bone artifact and its superior soft tissue contrast.
- MR scan of the craniospinal axis should be explored for parameningeal RMS to exclude leptomeningeal spread.
- CT chest, abdomen and pelvis
- PET-CT scan: the role of PET-CT is unclear in the initial staging evaluation, but RMS is an FDG avid tumor and PET-CT effectively demonstrates lymphatic and distant metastases missed by conventional imaging methods.
- Bone scan: has been traditionally been included in staging workup of RMS in adult patients, but is no longer used for pediatric patients.
- Bone Marrow biopsy
- Bone marrow biopsy has traditionally been included in the staging workup of RMS.
- Whether bone scans and bone marrow biopsies may be avoided in selected patients with favorable characteristics remains unknown and will require confirmation in prospective studies.
- Lumbar puncture
- Generally not necessary in most patients. The 2 exceptions are:
- Patients with parameningeal primary RMS, including middle ear, nasal cavity, paranasal sinus, nasopharynx and infratemporal fossa sites.
- Patients with evidence of meningeal invasion by imaging studies.
Diagnostic material should be reviewed by a pathologist with expertise in bone and soft tissue sarcoma to confirm the diagnosis.
- IHC is used to identify muscle-specific proteins such as actin, myosin, myoglobin, Z-band protein and myogenic differentiation (MyoD1 and myogenin – these two are the most sensitive and specific stains for RMS).
- Other IHC stains may be useful in the differential diagnosis of tumors that present as small round blue cell tumors.
- FISH, RT-PCR, NanoString or NGS to identify FOXO1 rearrangements creating PAX-FOXO1 fusion transcripts in alveolar RMS.
The current standard of care for RMS is multimodality approach to therapy, which has resulted in significant improvement in overall survival of RMS patients. Treatment includes chemotherapy, and definitive local therapy consisting of surgery (if feasible) and radiation therapy.
For the most current approach to pediatric RMS please contact the oncologists at BC Children’s Hospital.
Treatment is individualized based on presentation and site(s) of disease.
- Chemotherapy is used for primary cytoreduction and eradication of both macroscopic and microscopic metastatic disease.
- RMS is a very sensitive disease to chemotherapy. Provided patients are fit, intensive multiagent chemotherapy is initiated despite the presence of metastatic disease. (However, the presence of metastatic disease is a poor prognostic factor).
- In various retrospective studies of multidrug chemotherapy regimens in adult RMS, overall response rates have ranged from 82-86%, while 5 year overall survival ranged from 35%-47% (as compared to 5y OS of greater than 70% in children with non-metastatic RMS).
- Due to lack of data in adults, chemotherapy protocols for adult RMS are derived from pediatric studies.
- The current approach at BC Cancer is to recommend alternating cycles of vincristine/doxorubicin/cyclophosphamide with ifosfamide/etoposide for a total of 14 cycles.
- Where feasible, complete excision for localized disease is recommended, provided that functional and/or cosmetic results are acceptable. Given the varied potential sites of origin, surgery may not be feasible in some cases, for eg. in tumors arising in the head and neck.
Radiation therapy (RT)
- Radiation therapy is usually an essential treatment modality to enhance local control in patients with RMS.
- At BC Cancer, RT is usually introduced after the patient has received 4-5 cycles of multiagent induction chemotherapy.
- If leptomeningeal dissemination is demonstrated, then craniospinal radiation therapy is indicated for curative therapy.
- The majority of relapses occur within 2 years of initial diagnosis, with relapses generally being fatal. Late relapses (>5 years) are uncommon.
- Long-term survivors may develop late treatment related complications such as second malignancy, pathologic fractures and other radiation-related complications (eg. wound complications, pulmonary fibrosis, limb leg discrepancy, femoral head necrosis).
- Late chemotherapy-related complications include second malignancy, reduced fertility, renal insufficiency, cardiomyopathy and neuropathy.
Suggested follow-up regimen
Every 3 months for 2 years then every 6 months in years 3-5, then annually:
- Clinical and physical exam
- MRI or CT of primary site
- CT chest
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