Rethinking bone marrow biopsy: is PET/CT enough for staging low-grade follicular lymphomas?

This study evaluates the diagnostic performance of staging 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) for detecting bone marrow involvement (BMI) in low-grade follicular lymphoma (FL) and its impact on the clinical necessity of bone marrow biopsy (BMB). We retrospectively analyzed patients newly diagnosed with low-grade (grade 1-2) FL who underwent both F-FDG PET/CT and BMB from 2010 to 2022 at two Chinese institutions. PET/CT's diagnostic accuracy for BMI was assessed using BMB as gold standard. Clinical and imaging data were analyzed to identify risk factors for BMI. Among 171 patients, 27 had positive BMB results. PET/CT demonstrated 86.5% accuracy in detecting BMI. In patients with PET/CT-based stage I-II disease, all BMB results were negative. In contrast, among patients with PET/CT-based stage III-IV disease, BMB upstaged 13 to stage IV. In patients with advanced-stage disease as determined by PET/CT, four risk factors were significantly linked to BMB positivity: female sex, Eastern Cooperative Oncology Group performance score > 1, elevated beta2-microglobulin levels, and involvement of > 4 lymph node regions. Patients were stratified into low-, intermediate-, and high-risk groups with corresponding BMB-positive rates of 5.6%, 40.7%, and 68.8%, respectively. No survival differences were observed between BMB-positive and BMB-negative patients. PET/CT can safely and effectively substitute for BMB in the staging of early-stage, low-grade FL. However, in advanced-stage disease, BMB remains valuable for diagnosis. The rate of BMB positivity correlates with tumor burden -related risk factors.