Sydney 2005: Immunophenotype of the Malignant Clone – Implications on Management
By Jesus San Miguel, MD
Dr. San Miguel reviewed the use of immunophenotyping–usually restricted to research or to the diagnosis of unusual cases of MM – and the potential this technique has in daily practice. Immunophenotyping identifies the abnormalities in plasma cells and thus distinguishes between normal and malignant plasma cells. Identification of such differences in antigen profiles provides a means to distinguish between monoclonal gammopathy of undetermined significance (MGUS) and MM; MGUS patients routinely have greater than 5% normal plasma cells while MM patients routinely have less than 5% normal plasma cells. When assessing minimal residual disease (MRD), immunophenotyping applies to the vast majority of patients and is highly predictive or the risk of relapse. Dr. San Miguel discussed the results of more than 700 of his patients who were treated using the GEM2000 protocol. Antigen panels were obtained before chemotherapy was initiated; more than 90% of cases of malignant plasma cells had abnormalities in antigen expression. All MM patients were positive for CD38 and CD138 antigens; B-cell antigens were present in 5% to 20% of cases. They observed a down regulation of CD56 and CD117 correlated with a poor prognosis and shorter survival. Similarly, CD19 and CD28 were correlated with poor prognosis while CD20 and CD 35 had no influence on prognosis. These results support the clinical benefits of immunophenotyping MM patients.