Bone Marrow and Lymph Node Involvement in Newly Diagnosed Pediatric Rhabdomyosarcoma: Can 18F-FDG PET/CT Replace Bone Marrow and Lymph Node Biopsies? Analysis of the "Paris Kids Cancer" Cohort.

BACKGROUND

Accurate staging is critical in pediatric rhabdomyosarcoma (RMS), as bone marrow (BM) and nodal involvement strongly influence risk stratification and treatment. Current guidelines recommend invasive procedures, including bone marrow aspirate/biopsy (BMAB) for all patients, and nodal histology in selected patients, despite their burden in children. This study evaluates the diagnostic performance of 18F-FDG PET/CT for BM and nodal staging in pediatric RMS.

METHODS

A retrospective, multicenter study was conducted including patients less than 25 years with newly diagnosed RMS from Paris Kids Cancer centers who underwent baseline 18F-FDG PET/CT. PET/CT accuracy was assessed using BMAB as the reference standard. For nodal staging, histological confirmation was used when available; otherwise, an exploratory real-world clinical assessment of lymph node status based on imaging and follow-up was applied. Discordant cases underwent multidisciplinary review including MRI.

RESULTS

Among 147 patients, 129 had both 18F-FDG PET/CT and BMAB. PET/CT correctly classified BM status in more than 99% of cases, with a negative predictive value of 99.1%. Nine PET-positive/BMAB-negative cases were confirmed as true BM involvement on MRI, reflecting possible BMAB sampling bias. For nodal staging, 18F-FDG PET/CT sensitivity and specificity were 85.2% and 85.7% versus histology (48 cases). Using real-world clinical assessment (146 cases), sensitivity and specificity increased to 86.5% and 96.8%, respectively.

CONCLUSIONS

18F-FDG PET/CT demonstrates excellent accuracy for BM staging and strong performance for nodal assessment in pediatric RMS. These findings support selective omission of invasive staging procedures in patients with negative 18F-FDG PET/CT while reinforcing the complementary role of sentinel node biopsy in specific subgroups.