Determination of plasma cell secreting potential as an index of maturity of myelomatous cells and a strong prognostic factor.

ABSTRACT

According to the widely accepted myeloma staging system, the bulk of paraprotein is the main determinant of disease stage. However, myelomatous plasma cells differ considerably in their ability to synthesize and secrete monoclonal paraprotein. We determined plasma cell secreting potential (PCSP) as the amount of M-component, divided by the percentage of marrow plasmacytic infiltration, in 240 patients with myeloma, and correlated our results with chain isotype, plasma cell morphology, severity of bone disease, well-recognized prognostic factors, such as serum LDH, CRP, albumin and beta2-microglobulin, treatment response and overall survival. PCSP was higher in IgG than in other myeloma types, and was an almost constant parameter for each individual patient, in 134/166 cases. A > 10% decrease of PCSP in 26 patients was associated with disease aggressiveness and treatment failure. Patients with MGUS had significantly higher PCSP than those with myeloma of the same chain type. Higher PCSP was associated with stage I, absence of Bence-Jones proteinuria and indolent forms of disease with lower proliferating cell nuclear antigen (PCNA) positivity, serum LDH, alpha2-globulins, CRP and beta2-microglobulin and higher albumin levels. Conversely, patients with immature/plasmablastic morphology and those with severe bone disease had lower PCSP. Good responders to treatment had significantly higher PCSP than moderate and poor responders and PCSP was strongly correlated with overall survival in IgG and IgA myeloma. In conclusion, PCSP reflects the maturation status of myelomatous cells and therefore can be used as a prognostic factor, since patients with high secreting potential represent a lower malignancy group, in comparison to those with a low secreting potential.