We treated 103 multiple myeloma (MM) patients with 7 g/m2 cyclophosphamide (Cy) followed by 300 μg G‐CSF/d to harvest peripheral blood progenitor cells (PBPC). PBPC autografts containing > 2.0 × 106 CD34+ cells per kg body weight were obtained at the first attempt from 90/100 evaluable patients. The most significant factor predicting impairment of PBPC collection was the duration of previous melphalan treatment (P < 0.0001). In multivariate discriminate analysis, treatment with melphalan during the most recent chemotherapy cycles prior to mobilization (P = 0.0727) and previous radiotherapy (P = 0.0628) had a marginally significant negative influence on the efficacy of PBPC collection. We found no reduced functional capacity of CD34+ cells to restore haemopoiesis after myeloablative treatment related to the duration of melphalan exposure. At the time of best response to conventional treatment, a median paraprotein reduction of 21% was achieved following high‐dose cyclophosphamide (HD‐Cy). Two heavily pretreated patients died and one patient developed pulmonary toxicity W.H.O. grade IV following HD‐Cy. Potential transplant candidates should undergo mobilization and harvesting of PBPC before melphalan‐containing treatment. Combinations of haemopoietic growth factors and their dose modifications should be investigated to improve PBPC collection, to allow a dosage reduction of the mobilization chemotherapy.

We consider the qPCR to be an accurate method for assessing samples with low amounts of malignant cells.

Dose-escalated treatments, with particular regard to the inclusion or omission of TBI, should be prospectively investigated to find the best high-dose regimen.

Multiple myeloma (MM) is a B cell malignancy characterized by the accumulation of clonal plasma cells in the bone marrow (BM) secreting a monoclonal immunoglobulin. Due to the limited success of conventional chemotherapies in MM, intensified high-dose (HD) chemotherapy regimens followed by autologous hematopoietic stem cell transplantation are now widely used.

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