Circulating tumor plasma cells correlate with tumor burden and routine laboratory markers in newly diagnosed multiple myeloma

Circulating tumor plasma cells (CTPCs) detected by multiparameter flow cytometry may serve as a minimally invasive marker of disease burden in multiple myeloma (MM). However, the relationship between CTPC burden, routine laboratory parameters, and bone marrow (BM) involvement remains insufficiently characterized in regional clinical settings. This retrospective single-center study included 51 consecutive patients with newly diagnosed MM. Peripheral blood CTPCs were quantified using ten-color flow cytometry. Among them, 41 patients with evaluable CTPC data were stratified into CTPC-higher (n = 20) and CTPC-lower (n = 21) groups using a 0.07% cutoff. Laboratory variables and immunophenotypic features were compared between groups, and correlations were assessed using Spearman rank analysis. Exploratory logistic regression adjusted for age and sex was performed, and Benjamini-Hochberg false-discovery-rate correction was applied to multiple comparisons. Compared with the CTPC-lower group, the CTPC-higher group had lower hemoglobin levels (73.5 vs 107.0 g/L; P < .001), lower albumin levels (30.9 vs 38.2 g/L; P = .006), higher β2-microglobulin levels (6.97 vs 3.25 mg/L; P = .004), and higher BM plasma cell percentages on smear examination (34.75% vs 12.00%; P = .005). CTPC levels were positively correlated with BM plasma cell percentage on smear examination (ρ = 0.67; P < .001) and negatively correlated with hemoglobin levels (ρ=-0.68; P < .001). These group differences and correlations remained significant after false-discovery-rate correction (all q ≤ 0.018). In age- and sex-adjusted analyses, hemoglobin, albumin, β2-microglobulin, and BM plasma cell percentage on smear remained associated with CTPC-higher status. Higher peripheral blood CTPC levels were associated with greater BM tumor burden and more abnormal routine laboratory markers in patients with newly diagnosed MM. CTPC quantification may serve as an adjunctive marker for baseline disease assessment in regional clinical settings. These cross-sectional findings from this limited sample do not establish prognostic value.