Prognostic impact of beta-2 microglobulin in patients with extranodal natural killer/T cell lymphoma

Although serum beta-2 microglobulin (B2M) has been suggested as an independent prognostic factor for several lymphoproliferative diseases, it has rarely been investigated in extranodal natural killer/T cell lymphoma (ENKTL). From a prospectively collected database, 145 patients with ENKTL were identified. Among them, a total of 101 patients were included in the analysis, with exclusion of patients without baseline serum B2M level and those did not receive anticancer therapy. Serum B2M (<3.0 vs. ≥3.0 mg/L) was analyzed for association with overall survival (OS). Seventy-nine (78 %) patients had nasal ENKTL, and 22 (22 %) had extranasal ENKTL. In overall patients, median OS was 26.7 months (95 % confidence interval (CI), not assessable), with a median follow-up of 32.4 months (range, 0.9-155.2 months). While median OS was not reached in patients with nasal ENKTL, extranasal ENKTL group had median OS of 5.1 months (95 % CI, 1.2-8.9 months; p < 0.001). Baseline serum B2M was significantly associated with OS in patients with nasal ENKTL (p < 0.001). This was consistent in limited (stages I and II) nasal ENKTL (p = 0.002) and disseminated (stages III and IV) nasal ENKTL (p = 0.02). However, there was no difference of OS in extranasal ENKTL patients (p = 0.69). In multivariate analysis including other prognostic factors, elevated serum B2M was significantly associated with poor OS (hazard ratio (HR) = 3.8, 95 % CI 1.7-8.2, p = 0.001, in a model including Korean Prognostic Index, and HR = 3.6, 95 % CI 1.6-8.2, p = 0.002, in a model including International Prognostic Index). In patients with nasal ENKTL, baseline serum B2M is a powerful prognostic factor. The prognostic value of B2M was independent of previously established prognostic models. Further investigations are necessary to validate the role of B2M in ENKTL.