Evaluation of bone marrow involvement in extranodal NK/T cell lymphoma by FDG-PET/CT

Evaluation of bone marrow involvement (BMI) by conventional bone marrow biopsy (BMB) can generate false-negative results if marrow disease is focal. The sensitivity of 18F-2-fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography (FDG-PET/CT) in assessing BMI in extranodal NK/T cell lymphoma (ENKL) has not been determined. We retrospectively collected clinical data from a series of 55 patients with newly diagnosed ENKL, who have received both FDG-PET/CT and BMB prior to treatment. BMB results were used as reference standard. Twelve patients (21.8 %) were considered positive lymphomatous infiltration by FDG-PET/CT (PET-CT/BM+), and five patients (9 %) were identified positive by BMB (BMB/BM+). There was a discordant result in seven patients who were PET-CT/BM+ but BMB/BM-. The sensitivity and specificity of FDG-PET/CT for identifying BMI were 100 and 86 %, respectively. Then, we analyzed the overall survival (OS) and progression-free survival (PFS) of patients who were PET-CT/BM+ and PET-CT/BM-. The median follow-up time was 16 months (range, 3 to 43 months). PET-CT/BM+ patients possessed worse 2-year OS than PET-CT/BM- patients (84.8 vs 67.9 %, P < 0.05). The estimated 2-year PFS for PET-CT/BM- and PET-CT/BM+ patients were 72.7 and 41.9 % (P < 0.05), respectively. However, it was hard to conclude that patients who were PET-CT/BM+ had similar survivals to advanced-stage patients due to the low number of patients who were PET-CT/BM+. In conclusion, FDG-PET/CT can complementally detect positive BMI patients missed by BMB in ENKL. The utility of FDG-PET/CT for defining bone marrow status has important prognostic value.