A review of the cytokine network in multiple myeloma

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Abstract
Because many studies have focused on growth factors in multiple myeloma, the study of the cytokine network appears to be useful for this purpose. Interleukin‐6 (IL‐6) and IL‐2 with their soluble receptors (IL‐3, IL‐4, IL‐10, and IL‐11) have been examined. Plasma cells may produce IL‐6 by an autocrine mechanism whereas a paracrine mechanism is believed to be involved in the production of IL‐6 by bone marrow stromal cells through an interaction between adhesion molecules present on myeloma plasma cells and their respective receptors that are present on bone marrow stromal cells. In addition, control over production of IL‐6 may be exerted by other ILs such as IL‐1β and IL‐10. Among target cells, the growth of normal and myeloma plasma cells is supported by IL‐6, which also induces the differentiation of myeloma plasmablastic cells into mature plasma cells. This last action also is shared by IL‐3, IL‐4, and, most likely, IL‐8. Evaluation of the serum level of IL‐6, C reactive protein, soluble IL‐6 receptor (sIL‐6R), and soluble IL‐2 receptor (sIL–2R), together with the activity exerted by IL‐3 and IL‐4 on some cellular subsets, may constitute an additional element in the differential diagnosis of borderline cases. However, the concomitant evaluation of all immunologic parameters could be more useful than the value of a single IL. Serum levels of IL‐6, sIL‐6R, sIL‐2R, and the expression of membrane‐bound IL‐2 receptors, both on bone marrow plasma cells and on peripheral blood mononuclear cells, are correlated with disease activity and disease stage. In addition, IL‐6 and sIL‐6R serum levels are believed to be correlated with the duration of disease‐free survival because a high serum level at the time of diagnosis is believed to be correlated with a short duration of survival. However, some laboratory parameters may express the same prognostic value as high β2 microglobulin and lactate dehydrogenase (LDH) serum levels together with a high plasma cell labeling index are correlated with disease activity. Furthermore, if the evaluation is performed at the time of diagnosis, high values of these parameters are correlated with a short disease‐free survival. A correlation between laboratory parameters and the serum level of several cytokines was demonstrated. Hence, the real advantage of the prognostic evaluation of cytokines is reserved for patients who do not exhibit uniform results with regard to β2 microglobulin and LDH serum levels, or, better, for borderline cases. With regard to the differential diagnosis, all immunologic parameters should be evaluated concomitantly rather than separately to confer a real prognostic value to results. Furthermore, a particular relation was found between a high sIL‐6R serum level and a poor response to chemotherapy, therefore suggesting the possibility of identifying in advance a subset of patients with a high risk of treatment failure, as has already been demonstrated in other hematologic malignancies. Finally, the majority of studies indicate that interferons are used mainly in the immunotherapy for multiple myeloma, whereas many clinical trials should still be required for the evaluation of the effectiveness of anti‐I‐L6 antibodies or antiidiotypic vaccines in reference to the eligible patients for these particular therapies. Cancer 2003;97:2440–52. © 2003 American Cancer Society. DOI 10.1002/cncr.11072