Assessment of Bone Marrow Involvement in Extranodal NK/T-Cell Lymphoma: Positron Emission Tomography versus Bone Marrow Biopsy, and the Significance of Minimal Involvement by EBV+ Cells (KROG 18-09).

PURPOSE: This study aims to investigate the diagnostic significance of PET/CT in assessing bone marrow (BM) involvement through a comparison of PET/CT findings with BM biopsy in extranodal NK/T-cell lymphoma.

MATERIALS AND METHODS: The medical records of 193 patients were retrospectively reviewed. Patients were categorized as having early-stage (PET-ES) or advanced-stage (PET-AS) disease based on PET/CT results. The BM involvement was classified into three groups according to BM biopsy: gross BM involvement, minimal BM involvement (defined as the presence of a limited number of EBV+ cells in BM), and no involvement. Calculations of the accuracy of PET/CT in detecting BM involvement and analysis of the clinical outcomes (progression-free survival [PFS] and overall survival [OS]) according to the BM biopsy status were performed.

RESULTS: PET/CT exhibited a sensitivity of 64.7% and a specificity of 96.0% in detecting gross BM involvement. For detecting any (both gross and minimal) BM involvement, the sensitivity was 30.4%, while the specificity was 99.0%. Only one (0.7%) patient demonstrated gross BM involvement among the PET-ES group. Survival outcomes of the PET-ES group with minimal BM involvement (3-year PFS 55.6%, OS 77.0%) were closer to those of the PET-ES group with no BM involvement (3-year PFS 62.2%, OS 80.6%) than to those of the PET-AS group (3-year PFS 20.1%, OS 29.9%).

CONCLUSION: PET/CT exhibits high specificity, but moderate and low sensitivity in detecting gross and minimal BM involvement, respectively. The clinical significance of minimal BM involvement for patients in the PET-ES group may be limited.