Preliminary results of positron emission tomography with F-18-fluorodeoxyglucose (PET/CT-FDG) in initial staging and treatment assessment of childhood rhabdomyosarcoma

Abstract

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Objectives: Childhood rhabdomyosarcoma, a soft tissue malignant tumor of skeletal muscle origin, accounts for approximatively 3.5 % of cases of cancer among children of 0 to 14 years. Children with metastatic disease at diagnosis have a poor prognosis. This study compared prospectively PET-FDG with conventional imaging in initial staging and early chemotherapy evaluation of childhood rhabdomyosarcoma.

Methods: Patients (pts) with pathologically-proven rhabdomyosarcoma underwent computed tomography, MRI, ultrasonography and PET-FDG imaging at baseline and after 3 courses of chemotherapy. Efficacy analysis was based on conventional imaging results only. PET/CT imaging was performed 60 to 90 min after iv injection of 5 MBq/kg of F-18-FDG. Tumor response was evaluated by conventional imaging analysis according to RECIST criteria and by PET-FDG visually and with standardized uptake value (SUV) normalized for body mass as complete response (CR) (SUV < regional background), incomplete response (IR) (improved images but persistent abnormal uptake), and no response (NR).

Results: Nine pts (2F and 7M, 1-14 years), were studied, including 4 embryonal and 5 alveolar rhabdomyosarcomas. Initial conventional imaging showed local lymph nodes in 2 pts, distant lymph nodes in 3 pts and no metastasis in the others. PET-FDG confirmed all pathological sites, with mean SUV ranging from 1.86 to 5.24 and max SUV from 2.69 to 8.85. PET-FDG revealed additional distant metastases (bone and lung) in 2/9 pts with therapeutic impact in one case. Results of early evaluation after 3 courses of chemotherapy are summarized in the table. [Table].The main discordance was in the interpretation of PR. On the 5 pts interpreted as CRs by FDG-TEP, 2 were confirmed as CRs by follow-up, 1 has not been evaluated yet and 1 was considered as a PR by follow-up. The last one was a false negative on FDG-PET with residual tumor in the urinary tractus. The NR patient considered as IR on FDG-PET became a PR on MRI in the follow-up.

Conclusions: These preliminary results showed a benefit of PET-FDG in initial staging and early chemotherapy assessment in childhood rhabdomyosarcoma. Follow-up will confirm the predictive value of early FDG-PET.