FDG-PET for staging of rhabdomyosarcoma

8545 Background: Complete staging of rhabdomyosarcoma is critical for delivery of appropriate therapy. Current diagnostic tools have known limitations. We have evaluated the role of 18F fluorodeoxyglucose positron emission tomography (PET) in the staging of patients with rhabdomyosarcoma. Methods: Since 1997, 60 patients with rhabdomyosarcoma underwent 159 PET scans. Of these, 21 patients with a median age of 11 years had a PET scan as part of their initial staging evaluation, before or within 13 days of initiation of therapy. Twelve patients had alveolar and 9 had embryonal histology. Primary sites included parameningeal (11), extremity (4), trunk (3), bladder/prostate (2), and head and neck (1). Results from CT, MRI, bone scan, and pathology within 1 month of the PET were compared. Results: A total of 83 sites were evaluated. All 21 patients had positive PET scans at the primary site. Twenty six PET positive sites at primary or nodal regions were biopsied and in all sites disease was confirmed. Standardized uptake value (SUV) for the primary site at the time of diagnosis ranged from 2.4 to 12.7 (mean 5.7). All SUVs prior to therapy were ≥4. There was no significant difference in SUV when evaluated by primary site or histology. PET showed involvement of regional lymph nodes in 12 patients. Five of the 12 patients underwent lymph node biopsy, all confirming involvement. In 3 of these cases, CT or MRI failed to detect the regional involvement identified on PET. At 11 sites, CT or MRI was equivocal for detection of regional or distant spread. In these cases, PET confirmed disease in one case and excluded disease in 10 cases. PET failed to capture sites of disease visualized by CT, MRI, or bone scan at 10 sites, including pelvic, paraaortic, mediastinal, cervical and retropharyngeal lymph nodes as well as vertebral bodies. When comparing PET to the final clinical determination of disease extent, PET was 83% sensitive and 97% specific. Conclusion: These preliminary data indicate that PET is a useful adjunct in the initial staging of rhabdomyosarcoma. In 3 of 21 cases (14%), therapy was altered because of nodal disease detected only on PET. A prospective study of PET for staging of rhabdomyosarcoma is warranted. No significant financial relationships to disclose.