B2M and extranodal nasal NK/T cell lymphoma: Previous studies suggested serum beta-2 microglobulin level as a potential prognostic biomarker of diverse lymphoproliferative disorders, including Hodgkin lymphoma [24, 25], mucosa-associated lymphoid tissue lymphoma [26, 27], DLBCL prior to the rituximab era [16, 28], mantle cell lymphoma [29, 30], and nasal NK/T-cell lymphoma [31, 32].