Before a biopsy of a suspected tumor mass is performed, imaging studies of the mass and baseline laboratory studies should be obtained. After the diagnosis of rhabdomyosarcoma has been made, an extensive evaluation to determine the extent of the disease should be done prior to instituting therapy. This evaluation should include a chest x-ray, computed tomography (CT) scan of the chest, bilateral bone marrow aspirates and biopsies, bone scan, magnetic resonance imaging (MRI) of the base of the skull and brain (for parameningeal primary tumors only), and CT scan of the abdomen and pelvis (for lower extremity or genitourinary primary tumors).
A CT or MRI scan of regional lymph nodes should be considered. Abnormal-appearing lymph nodes should be biopsied when possible. One study has demonstrated that sentinel lymph node biopsies can be safely performed in children with rhabdomyosarcoma, and tumor-positive biopsies may alter the treatment plan. Positron emission tomography (PET) with fluorine-18-fluorodeoxyglucose (FDG) scans can identify areas of possible metastatic disease not seen by other imaging modalities.[2-4] However, the efficacy of these two procedures for identifying involved lymph nodes or other sites is currently under investigation, and these procedures are not required by current treatment protocols.
Terms used in this summary section are defined below in Table 1.Table 1. Definition of Terms
|Favorable site||Orbit; nonparameningeal head and neck; genitourinary tract other than kidney, bladder, and prostate; biliary tract.|
|Unfavorable site||Any site other than favorable.|
|T1||Tumor confined to anatomic site of origin (noninvasive).|
|T2||Tumor extension and/or fixation to surrounding tissue (invasive).|
|a||Tumor ≤5 cm in maximum diameter.|
|b||Tumor >5 cm in maximum diameter.|
|N0||No clinical regional lymph node involvement.|
|N1||Clinical regional lymph node involvement.|
|NX||Regional lymph nodes not examined; no information.|
|M0||No metastatic disease.|
Staging of rhabdomyosarcoma is relatively complex. The process includes the following steps:
- Assigning a Stage: Determined by primary site, tumor size (widest diameter), and presence or absence of regional lymph node and/or distant metastases.
- Assigning a local tumor Group: Determined by status postsurgical resection/biopsy, with pathologic assessment of the tumor margin and of lymph node disease.
- Assigning a Risk Group: Determined by Stage, Group, and histology.
As noted previously, prognosis for children with rhabdomyosarcoma depends predominantly on the primary site, tumor size, Group, and histologic subtype. Favorable prognostic groups were identified in previous Intergroup Rhabdomyosarcoma Study Group (IRSG) studies, and treatment plans were designed on the basis of assignment of patients to different treatment groups according to prognosis. Several years ago, the IRSG merged with the National Wilms Tumor Study Group and two large cooperative pediatric cancer treatment groups to form the Children's Oncology Group (COG). New protocols for children with soft tissue sarcoma are developed by the Soft Tissue Sarcoma Committee of the COG (COG-STS).
Current COG-STS protocols for rhabdomyosarcoma use the TNM-based pretreatment staging system that incorporates the primary tumor site, presence or absence of tumor invasion of surrounding tissues, tumor size, regional lymph node status, and the presence or absence of metastases. This staging system is described in Table 2 below.[5,6]Table 2. Soft Tissue Sarcoma Committee of the Children's Oncology Group: Pretreatment Staging System
|Stage||Sites of Primary Tumor||T Stage||Tumor Size||Regional Lymph Nodes||Distant Metastasis|
|N0 = absence of nodal spread; N1 = presence of regional nodal spread beyond the primary site; X = unknown N status; M0 = absence of metastatic spread; M1 = presence of metastatic spread beyond the primary site and regional lymph nodes; T1 = tumor confined to anatomic site of origin (noninvasive); T2a = tumor extension and/or fixation to surrounding tissue (invasive), tumor ≤5 cm in maximum diameter; T2b = tumor extension and/or fixation to surrounding tissue (invasive), tumor >5 cm in maximum diameter.|
|1||Favorable sites||T1 or T2||Any size||N0 or N1 or NX||M0|
|2||Unfavorable sites||T1 or T2||a, ≤ 5 cm||N0 or NX||M0|
|3||Unfavorable sites||T1 or T2||a, ≤ 5 cm||N1||M0|
|b, > 5 cm||N0 or N1 or NX|
|4||Any site||T1 or T2||Any size||N0 or N1 or NX||M1|
The IRS-I, IRS-II, and IRS-III studies prescribed treatment plans based on the Surgical-pathologic Group system. In this system, Groups are defined by the extent of disease and by the completeness or extent of initial surgical resection after pathologic review of the tumor specimen(s). The definitions for these Groups are shown in Table 3 below.[7,8]Table 3. Soft Tissue Sarcoma Committee of the Children's Oncology Group: Surgical-pathologic Group System
|I||Approximately 13%||Localized tumor, completely removed with microscopically clear margins and no regional lymph node involvement. Lymph node biopsy or sampling is encouraged if lymph nodes are clinically or radiographically suspicious.|
|II||Approximately 20%||Localized tumor, completely removed with: (a) microscopic disease at the margin, (b) regional disease with involved, grossly removed regional lymph nodes without microresidual disease, or (c) regional disease with involved nodes, grossly removed but with microscopic residual and/or histologic involvement of the most distal node from the primary tumor.|
|III||Approximately 48%||Localized tumor, incompletely removed with gross, residual disease after: (a) biopsy only, or (b) gross major resection of the primary tumor (>50%).|
|IV||Approximately 18%||Distant metastases are present at diagnosis. This category includes: (a) radiographically identified evidence of tumor spread, and (b) positive tumor cells in cerebral spinal fluid, pleural, or peritoneal fluids, or implants in these regions.|
After patients are categorized by Stage and Surgical-pathologic Group, a Risk Group is assigned. This takes into account Stage, Group, and histology. Patients are classified for protocol purposes as having a low risk, intermediate risk, or high risk of disease recurrence.[9,10] Treatment assignment is based on Risk Group, as shown in Table 4. To be designated as alveolar, the tumor must have greater than 50% alveolar elements; if the alveolar component is 50% or less, the tumor is considered embryonal.Table 4. Soft Tissue Sarcoma Committee of the Children's Oncology Group: Rhabdomyosarcoma Risk Group Classification
|Low risk||Embryonal||1||I, II, III|
|Embryonal||2, 3||I, II|
|Intermediate risk||Embryonal||2, 3||III|
|Alveolar||1, 2, 3||I, II, III|
|High risk||Embryonal or Alveolar||4||IV|
[Note: Since 2006, patients with undifferentiated sarcomas are treated on the COG-STS protocol for nonrhabdomyosarcomatous soft tissue sarcoma. Refer to the PDQ summary on Childhood Soft Tissue Sarcoma for more information.]References
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