Objective: To define progression factors of MGUS and SP in population of Gomel region in Belarus.

Case report: Solitary plasmacytoma (SP) and monoclonal gammopathy of undetermined significance (MGUS) are characterized by the presence of less than 10% of tumor cells in the bone marrow and the absence of CRAB criteria. Both diseases have a high risk of progression to multiple myeloma due to certain factors.

Methodology: The study included 106 patients: MGUS (n=90) and SP (n=16) of Gomel region (Belarus) in 2017–2019. The average age was 60.5 years; female patients prevailed All patients underwent aspiration biopsy with IPT and FISH, trepanobiopsy of the ilium wing with immunohistochemical examination of the bone marrow. (Bone marrow aspirates IPT and FISH, and biopsies were obtained for cytological and histopathological evaluation of PC infiltration, including immunohistochemical). The determination of the ratio of light chains of immunoglobulins (kappa/lambda) in blood serum was carried out. Results were assessed after 3 years of observation. The signs of progression include the appearance of any one of the CRAB-criteria.

Results: There were no statistically significant differences between groups of patients with MGUS and SP according to signs (presence of tumor plasma cells, CD95+, CD200+, CD27+, CD56+, IHC of CD138+ plasma cells, presence of M-protein in bone marrow) (Fisher p ranged from 0.292 to 0.73). An aberrant phenotype or the presence of clonal plasma cells <10% in SP patients was detected in 31%. According to the secretion of immunoglobulins: with MGUS, IgG secretion (53.3%) was most common, with SP, we observed non-secretion variant (37.5%), IgG secretion (31.5%). During the observation period, disease progression into MM was recorded in 18.8% in SP and in 16% MGUS patients. Disease progression in SP patients was associated with the presence of cytogenetic changes (the presence of del13) in combination with IHC of CD138+ >10%, an abnormal ratio of κ/λ chains. High expression of CD27+ was observed. In one patient with SP (iliac plasmacytoma), the disease transformed into MM within six months in the presence of risk factors: clonal plasma cells in the bone marrow −3.1%, CD56+ 93.1%, CD95+ 3.8% by IPT, del13, IHC CD138+ 20%. With MGUS, disease progression was associated with the presence of a combination of CD138+ >10% (76.5% vs. 23.6%; p<0.0001), CD95+ <20% (44.0% vs. 71.4%; p<0,083), CD56+ >20% according to IPT (27.3% vs. 78.0%; p<0.0001), loss of CD27+ expression (66.7%), abnormal ratio κ/λ of chains p<0.001.

Conclusion: Our study showed that a combination of such indicators as the presence of cytogenetic changes (in particular, the presence of del13), CD138+ cells >10% according to IHC, CD56+ >20%, CD95+ <20% according to IPT in combination with an abnormal ratio of κ/λ chains can have prognostic value in transformation into MM in both MGUS patients and SP patients.