Secondary monoclonal gammopathy of undetermined significance is frequently associated with high response rate and superior survival in patients with plasma cell dyscrasias.

Secondary monoclonal gammopathy of undetermined significance (MGUS) is a special phenomenon that occurs during the treatment of multiple myeloma (MM). The incidence, biological characteristics, and prognostic value of secondary MGUS in patients with MM remain undefined. We proceed with a retrospective systematic review of serum immunofixation electrophoresis studies performed in 438 cases of patients with plasma cell dyscrasias, including 409 cases of newly diagnosed MM and 29 cases of primary plasma cell leukemia. Secondary MGUS was more common in patients with myeloma who had undergone stem cell transplantation than in those who had not (17 [29.8%] of 57 versus 5 [1.4%] of 352, P < .001). The clinical parameters and cytogenetic characteristics in patients with or without secondary MGUS were comparable. The complete response rates in patients with or without secondary MGUS were 81.8% and 21.8% respectively (P < .01). For the cohort as a whole, secondary MGUS was associated with significantly prolonged progression-free survival (median, 52.0 months versus 22.5 months; P = .002) and overall survival (median, not reached versus 35.0 months; P < .001). The presence of secondary MGUS retained independent prognostic value with a moderate impact on overall survival (hazard ratio .128 [95% confidence interval .018 to .922]; P = .041) in the multivariate Cox regression model. However, when analysis was restricted to patients undergoing stem cell transplantation, no statistical differences in progression-free survival and overall survival were found. In conclusion, we observe that secondary MGUS was frequently observed in MM patients after transplantation and conferred a survival prolongation. The favorable survival in patients with secondary MGUS may be explained by beneficial effect from myeloablative therapy.