FDG PETCT for assessing marrow involvement at staging pediatric nonhematological round cell malignancies

Bone and lung are the common sites of metastasis in pediatric round cell tumors and its presence indicates poor outcomes. Staging workup for these malignancies thus includes bone marrow biopsy (BMB) along with evaluation of thorax, and tissue analysis for N MYCN status in neuroblastoma. BMB is an invasive procedure requiring general anesthesia with known disadvantages.With an aim of avoiding an invasive BMB a study was taken up to evaluate efficacy of FDG PET CT in detecting marrow involvement in neuroblastoma and rhabdomyosarcoma at staging.

Prospective observational study evaluated 83 newly diagnosed treatment naïve patients of neuroblastoma (n = 43) and rhabdomyosarcoma (n = 42) who underwent conventional imaging of PETCT with CECT of local region along with a CT thorax and BMB (both iliac crest) done within 1 week. Findings of FDG PETCT were compared with bone marrow histology and accuracy parameters were calculated.

The overall sensitivity, specificity, accuracy, positive-predictive value (PPV), negative-predictive value (NPV) of FDG PETCT for detection of marrow disease was 100%, 86.1%, 89.4%. 68.9% and 100%, respectively. Subset analysis showed sensitivity, specificity, PPV and NPV of 100%, 66%, 71.4% and 100%, respectively, for neuroblastoma, with rhabdomyosarcoma patients having few events NPV of 100% accuracy of 97.6%.

FDG PETCT with sensitivity and NPV of 100% can be considered as a first stop imaging and biopsy can be avoided in patients with a negative scan.