Multiple myeloma: Relationship between light chain isotype suppression, labelling index of plasma cells, and CD38 expression on peripheral blood lymphocytes

Abstract

In this study we have investigated the relationship between the labelling index of plasma cells, the expression of CD38 positive lymphocytes in the peripheral blood, and light chain isotype suppression. This study confirms the relationship between plateau‐phase disease and light chain isotype suppression (LCIS) and documents an inverse relationship between LCIS and CD38 positive lymphocytes (.001 < P < .01), which is similar to the relationship we have described with the expression of CD10 positive lymphocytes. PCA‐1 is rarely expressed in the peripheral blood of patients with myeloma and does not fulfill a role as a marker of active vs. stable disease. There is no relationship between the labelling index of plasma cells and LCIS, because many patients can enter a stage of progressive disease and yet have a labelling index of <1% at that time, although a labelling index <1% is present in the majority of patients with LCIS. β‐2‐microglobulin (β2M) also fails to differentiate these two phases of disease in myeloma and does not have a relationship with LCIS, CD38 expression, or CD10 expression. These data suggest that myeloma, like chronic granulocytic leukemia (CGL), can be considered as having two phases of disease: a stable or chronic phase disease, as identified by the presence of LCIS, the absence of CD10 and CD38 positive lymphocytes in the peripheral blood, and a low labelling index, and progressive disease, which is associated with the loss of LCIS and of, CD10 and CD38 positive lymphocytes in the peripheral blood and a high labelling index, although in many cases of progressive disease, the labelling index may also be low. β2M does not differentiate between these states.