Monoclonal gammopathy of undetermined significance (MGUS) in patients with solid tumors: effects of chemotherapy on the monoclonal protein.

The aim of this study was to assess the effect of systemic chemotherapy on the monoclonal protein levels of patients with solid tumors who also have a monoclonal gammopathy of undetermined significance (MGUS). All patients with solid tumors who were referred to our department for consideration of systemic chemotherapy were evaluated with serum protein electrophoresis (SPEP) for the presence of MGUS. When MGUS was confirmed with immunofixation, serial SPEP was performed during and after completion of chemotherapy. Over a 6-year period, 21 patients with solid tumors and MGUS were prospectively identified and assessed. At least 50% reduction of serum monoclonal protein was noted in 4 of 11 patients treated with paclitaxel or docetaxel with a platinum analogue and in 5 of 7 patients who received an irinotecan-containing regimen. Our data indicate that in MGUS patients treated with irinotecan-containing chemotherapy regimens, a high incidence of reduction in their monoclonal protein levels is observed. Since topotecan, another topoisomerase I inhibitor, has some activity in multiple myeloma, further evaluation of irinotecan may be warranted. Evaluation of larger numbers of MGUS patients treated with chemotherapy for their underlying malignancy may help identify "in vivo" potentially active agents and regimens for patients with overt myeloma.