FDG PET May Help Avoid Marrow Sampling in Rhabdomyosarcoma

Bone marrow aspirates and biopsies (BMAB) may be omitted in patients with FDG-avid primary rhabdomyosarcoma when pretreatment whole-body fluorodeoxyglucose positron emission tomography (FDG PET) shows no FDG-avid marrow disease, according to an international retrospective study published in the Journal of Clinical Oncology.

Investigators collected data from 18 institutions in Europe and North America. Eligible patients were aged 40 years or younger, had histologically confirmed rhabdomyosarcoma, and underwent FDG PET/computed tomography or PET/magnetic resonance imaging and direct bone marrow assessment at diagnosis. Among 403 patients considered in the analyses, the primary diagnostic analysis included 301 with FDG-avid primary tumors who underwent PET and BMAB before chemotherapy and tumor resection.

Bone marrow metastases were identified by both PET and BMAB in 54 patients, by PET alone in 24, and by BMAB alone in one. Both methods were negative in 222 patients. When BMAB was treated as the reference standard, PET had 98% sensitivity (95% CI, 90%-100%) and 90% specificity for detecting bone marrow metastases.

FDG-avid marrow disease was limited to one to five foci in approximately one-third of affected patients. Patients with disease detected by both PET and BMAB had more FDG-avid marrow foci, more metastatic sites, and lower survival than those with PET-positive but BMAB-negative findings, suggesting more advanced disease stages in the concordant-positive group.

Limitations included the retrospective design, enrichment for metastatic or FOXO1-rearranged disease, limited MRI data, and a lack of biopsy confirmation for FDG-avid marrow sites. BMAB samples were also frequently inadequate. The investigators concluded that marrow sampling may be omitted when appropriately performed PET shows no FDG-avid marrow disease. PET-positive lesions may warrant further evaluation with focused MRI or biopsy.

Source: Mercolini F, Just M, Shulkin BL, et al. Omitting bone marrow sampling in FDG-avid rhabdomyosarcoma with 2-[18F]FDG PET-negative marrow: results from an international retrospective study. J Clin Oncol. Published online August 24, 2026. doi:10.1200/JCO-25-03080