Discordant response or progression in patients with myeloma treated with thalidomide-based regimens

Thalidomide-based regimens (TBR) are now widely used for the treatment of refractory multiple myeloma and have shown significant activity in newly diagnosed patients. In some patients with secretory disease, we observed discrepancies between the reduction of the monoclonal protein levels and the plasma cell infiltration in the bone marrow and/or extramedullary sites of relapse after treatment with TBR. The purpose of this study was to assess the incidence and analysis of this phenomenon in all myeloma patients treated with TBR in our Institution.

We studied all patients who received TBRs and had a follow up time of at least 6 months. Partial response (PR) was defined as at least 50% reduction of serum myeloma protein and soft tissue plasmacytomas and/or > 90% reduction of Bence Jones protein excretion and minor response as a > 25% reduction of the serum myeloma protein or > 50% reduction of the Bence Jones myeloma protein.

Between July 1999 and July 2002 we treated 94 patients with advanced myeloma and 9 patients with newly diagnosed disease with TBR. Sixty-seven patients (66%) achieved either partial or minor response. In 4 patients (3 with advanced and 1 with newly diagnosed myeloma) the bone marrow was heavily infiltrated by plasma cells, despite a decrease of the paraprotein levels ranging from 38% to 68%. This discordance between monoclonal protein levels and bone marrow plasmacytosis was noted in 6% of patients rated as responders and in 11% of responding patients who actually had a repeat bone marrow assessment. Furthermore 6 responding patients, after achieving a PR which lasted between 5 and 9 months, relapsed with bone marrow (all cases), and extramedullary (2 cases) plasmacytosis, without increase of serum and/or urine monoclonal protein. This hyposecretory conversion was noted in 12.5% of relapsing patients.

Our data indicate that after treatment with TBR some patients with myeloma show discordant responses of the monoclonal protein levels and the bone marrow or extramedullary plasmacytosis. If our data are confirmed, they may have practical implications for assessment of response and follow up of patients treated with TBR.