A recent European study found that the percentage of plasma cells detected in a bone marrow sample is a strong predictor of multiple myeloma progression following stem cell transplantation.

Although the current definition for complete remission requires less than 5 percent of plasma cells in a bone marrow sample, the study’s authors found that patients with more than 1.5 percent bone marrow plasma cells were more likely to progress. Additionally, there was a trend toward shorter survival in these patients.

The study authors concluded that a bone marrow examination should be one of the first steps in estimating the amount of tumor remaining after stem cell transplantation.

The current criteria for complete remission include negative serum and urine immunofixation tests and less than 5 percent of bone marrow plasma cells. Immunofixation is a laboratory technique that may be used to detect the presence of antibodies produced by myeloma cells.

Although the current criteria are recommended by many of the world’s leading myeloma research groups, some in the myeloma community have suggested that the bone marrow examination is unnecessary for patients with negative immunofixation results. Opponents of the examination argue that the examination is not only uncomfortable for patients, but it is also not a proven prognostic factor for myeloma survival. Additionally, many find the 5 percent limit for bone marrow plasma cells to be arbitrary.

In order to determine the impact of bone marrow plasma cell count on patient long-term survival, physicians from the University of Barcelona, Spain, retrospectively analyzed data from 35 myeloma patients who underwent autologous stem cell transplantation between 1994 and 2008. After high-dose chemotherapy with melphalan ^[1] (Alkeran), all patients achieved negative immunofixation results and subsequently underwent bone marrow aspiration.

The median percentage of bone marrow plasma cells was 0.8 percent. The study authors acknowledged that their results were uncommonly low. They cited a recent report from the Mayo Clinic in which 14 percent of myeloma patients with negative immunofixation tests had 5 percent or more bone marrow plasma cells. The authors explained that the difference in results might be because the Mayo Clinic study included patients who achieved complete remission after chemotherapy or stem cell transplantation and the Mayo Clinic study included bone marrow biopsies, in addition to aspirates.

After statistically analyzing the data, the authors determined that a cutoff of 1.5 percent bone marrow plasma cells best predicted patient outcomes. Of the 35 patients in the study, 10 patients had more than 1.5 percent plasma cells in the bone marrow. Additionally, the percentage of bone marrow plasma cells after stem cell transplantation was similar regardless of whether patients were initially treated with chemotherapy or novel agents.

After a mean follow-up time of 7.3 years, the median progression-free survival for patients with 1.5 percent or less bone marrow plasma cells was not yet reached, compared to 3.1 years for patients with more than 1.5 percent bone marrow plasma cells.

Median overall survival has not yet been reached in patients with 1.5 percent or less bone marrow plasma cells and is 9.7 years in patients with more than 1.5 percent bone marrow plasma cells. Survival appears to be longer in patients with lower percentages of bone marrow plasma cells, but survival times for the two groups were not statistically different at the time of analysis.

For more information, see the study in the journal Biology of Blood and Marrow Transplantation ^[2] (abstract).