DNA aneuploidy, increased proliferation and nuclear area of plasma cells in monoclonal gammopathy of undetermined significance and multiple myeloma.
DNA cytometric and morphometric parameters of plasma cells were determined in 73 multiple myelomas (MMs), 31 monoclonal gammopathies of undetermined significance (MGUS), 11 reactive plasmacytoses (RPs) and 33 cases of normal bone marrow (NBM) using a TV-based static cytometer combined with a computerized relocation stage. Neoplastic transformation was defined by either an aneuploid DNA profile, an increased proliferative fraction or an increased mean nuclear area of plasma cells. Using threshold values defined by mean values and variations of NBM and RP, 67/73 MMs were correctly classified as malignant (sensitivity, 92%), whereas all NBMs and RPs were classified as benign (specificity, 100%). In MGUS, cytometric parameters of malignancy were detected in 19/31 cases (61%). Six of these cases developed MM after a median time of 4.9 years (mean follow-up, 9.3 years). Another three cases with MGUS developed MMs without previous cytometric plasma cell aberrations. Cytometric data from repeated measurements in MGUS progressing to MM exhibited perfect consistency over time concerning the presence or absence of cytometrically detected neoplastic transformation. Cytometric aberrations seem to be frequently associated with neoplastic growth in monoclonal plasma cell proliferations but do not predict clinically malignant behavior.