Detection of monoclonal plasma cells in the peripheral blood stem cell harvests of patients with multiple myeloma.

We evaluated the harvest product from 47 patients undergoing peripheral blood (BP) stem cell collections for monoclonal plasma cells (PC) using a sensitive immunofluorescence technique. 60% (28/47) had documented tumour cells in the apheresis product. The 32 patients in plateau had a mean of 1.62 x 10(6) PC/l v 74.64 x 10(6) in 15 relapsed patients (P < 0.01). 32% (6/19) of patients without any tumour cells in the initial sample had them detected on a subsequent apheresis sample. In four cases (all treated with GM-CSF) small numbers of tumour cells were detected initially but became undetectable on a subsequent sample.