Clinicopathological Features and Prognostic Differences Between Primary and Relapsed or Refractory Extramedullary Multiple Myeloma.

[PURPOSE] This study aims to explore the clinicopathological features related to extramedullary multiple myeloma (EMM) occurrence and evaluate prognosis differences between patients with primary EMM (PEMM) and those with relapsed or refractory EMM (R/REMM).

[PATIENTS AND METHODS] The laboratory test results, clinical, histopathological and immunophenotypic characteristics, cytogenetic changes and prognosis of 203 patients with MM were obtained. The patients were categorized into EMM+ and EMM- groups. Patients in the EMM+ group were further categorized into the PEMM and R/REMM groups based on the time of EMM occurrence, for further comparison.

[RESULTS] The incidence of EMM was 24.6% (50/203). Further classification of EMM showed that the incidence of PEMM was 16.3% (33/203), that of R/REMM was 8.4% (17/203).The proportion of CD20+ was significantly lower than that in the EMM- group (2.0% vs 15.0%, =0.013).In the EMM+ group,70% (35/50) of patients had elevated levels of β2-MG (≥ 5.5 mmol/L), and 24% (12/50) had elevated levels of serum calcium (> 2.65 mmol/L), higher than that in the EMM- group (41.2% and 12.4%, respectively), and the differences were statistically significant ( < 0.001 and = 0.049, respectively).Patients with R/REMM were more likely to have plasma cell leukemia and lower albumin levels than those with PEMM = 0.021 and 0.014, respectively). The median OS of patients in the EMM- group was longer than that of patients in the EMM+ group (59.6 vs 47.0 months, =0.197).The median OS of patients in the PEMM group was longer than that of patients in the R/REMM group and the difference was statistically significant (53.3 vs 30.5 months,= 0.015). Univariate and multivariate survival analyses revealed that R/REMM is an independent adverse prognostic factor ( = 0.003 and < 0.001 respectively),and PEMM was not associated with OS in patients with MM ( = 0.503 and = 0.545, respectively).

[CONCLUSION] R/REMM is an independent adverse prognostic factor for patients with MM. Patients with R/REMM are more likely to have plasma cell leukemia and lower albumin levels.