B2M and plasmacytoma: No significant differences between subgroups divided by the year of relapse (2003–2008, 2009–2014, and 2015–2021) were observed, except for the higher prevalence of extramedullary plasmacytomas at diagnosis and higher serum beta-2-microglobulin levels in patients identified with relapse in the most recent period between 2015 and 2021.