Normal plasma cells can be differentiated from multiple myeloma by their immunophenotype. Normal cells are CD45+, CD19+, CD20+, CD38++, CD56-/dim, CD138+, mIg- and polyclonal cIg. On the other hand, with multiple myeloma, plasma cells are monoclonal (cIg) and approximately 80% are CD19- CD56+ and 20% CD19- CD56-. The profile in plasma cell leukemia is similar to myeloma, but the CD56 is positive in 45% of cases. In the monoclonal gammopathy of undetermined significance there is a mixture of normal and neoplastic plasma cells. Residual disease in bone marrow is important to determine the efficacy of treatment and can be evaluated by flow cytometry or polymerase chain reaction of rearranged heavy chains of Ig. Flow cytometry has a sensitivity of 10-4 to 10-5, is performed in 2-3 hours and is applicable in 90% of cases. Qualitative PCR has a sensitivity of 10-6 and quantitative PCR of 10-5. Both tests are performed in 2-3 days and their applicability is around 75%.
Plasma cells; multiple myeloma; immunophenotype; flow cytometry; minimal residual disease
