Limited Benefit of Bone Marrow Biopsy in Extranodal NK/T-Cell Lymphoma in the PET/CT Era.

[RATIONALE AND OBJECTIVES] Positron emission tomography/computed tomography (PET/CT) is central to lymphoma staging, yet current guidelines still mandate bone marrow biopsy (BMB) for histologically confirming bone marrow infiltration (BMI, which defines stage IV disease) in the initial staging of extranodal NK/T-cell lymphoma (ENKTL). This study aims to compare the diagnostic accuracy and prognostic value of PET/CT and BMB in detecting BMI, and to evaluate whether BMB can be omitted in certain subgroups to refine staging protocols and avoid invasive procedures.

[MATERIALS AND METHODS] We conducted a retrospective cohort study of 133 treatment-naïve ENKTL patients who underwent concurrent PET/CT and BMB.

[RESULTS] BMB results were negative in all PET/CT-defined localized-stage patients (n=88) but positive in 15.6% (7/45) of advanced-stage cases. Using BMB as the reference standard, PET/CT showed high sensitivity (85.7%) and negative predictive value (NPV=98.9%), supporting disease exclusion. Specificity was 73.8%, accuracy 74.4%. In advanced disease, sensitivity remained 85.7%, NPV 95.7%, but specificity declined to 57.9%. Prognostically, PET/CT-defined BMI predicted inferior progression-free survival (PFS, hazard ratio [HR]=2.36, P=0.036) and overall survival (OS, HR=3.3, P=0.026), whereas BMB positivity showed limited prognostic discrimination (PFS HR=1.7, P=0.293; OS HR=3.08, P=0.039). Time-dependent area under the curve analysis demonstrated that PET/CT-detected BMI had consistent superiority in prognostic prediction across all follow-up intervals, a finding further substantiated by its higher C-index values for both PFS (0.63 vs. 0.55) and OS (0.69 vs. 0.60) compared to BMB. Notably, BMB results did not alter early/advanced staging or treatment allocation, but showed significant association with hemophagocytic lymphohistiocytosis (85.7% vs. 28.9%, P=0.015).

[CONCLUSION] PET/CT demonstrates high diagnostic and prognostic value in ENKTL staging, supported by an NPV of 98.9% and general alignment with therapeutic decision-making. Thus, routine BMB could potentially be omitted in the absence of unexplained cytopenias. Further validation in larger prospective cohorts is warranted before broad implementation.