Summary:superior to G-CSF alone based on mean CD34 ؉ cell yield per pheresis, adequate CD34 ؉ cell collections can be achieved with G-CSF alone in most MM patients The best method for peripheral blood progenitor cell (PBPC) mobilization in patients with multiple myeloma with less toxicity and with simplification of the procedure. (MM) remains controversial. We report the results of two different methods of PBPC collection for autologous Keywords: multiple myeloma; PBPC mobilization; GM-CSF; G-CSF transplantation in 40 patients with stage II or III MM. In group I (n = 18), HD-CY, 4 g/m 2 i.v., was administered followed by GM-CSF, 8 g/kg/day s.c., until the end of collection, starting the leukaphereses after hemaPeripheral blood progenitor cells (PBPC) are increasingly tological recovery (Ͼ1 × 10 9 /l WBC). In group II used for hemopoietic autologous rescue afer high-dose ther-(n = 22), G-CSF, 10 g/kg/day s.c., was used alone until apy (HDT) in multiple myeloma (MM). 1-7 The use of perthe last day of collection, starting consecutive aphereses ipheral blood as the source of hematopoietic stem cells has on the 5th day. A minimum of two aphereses were perreplaced the bone marrow due to the rapidity of the formed to collect at least 2 × 10 6 /kg CD34 + cells. Both engraftment and the difficulties in harvesting bone marrow patient groups were comparable for age, sex and clinical cells in most MM patients due to osteoporosis or to preprognostic features as well as previous therapies. In vious irradiation. Another potential advantage for the use group I, the median yields per pheresis were: MNC 1. 47 of PBPC is the lower percentage of tumor cell contami-(1.38-2.32) × 10 8 /kg, CFU-GM 0.82 (0.18-13.2) × 10 4 /kg nation when compared with bone marrow, as recently conand CD34 + cells 1.98 (0.96-6.96) × 10 6 /kg. In group II firmed by molecular methods, 8 although this point is conthese results were: MNC 2.44 (2.06-3.6 × 10 8 /kg) troversial because several recent reports have suggested that (P = 0.03), CFU-GM 0.75 (0.16-7.8) × 10 4 /kg and CD34 + plasma cells may be recruited into the peripheral blood after 1.05 (0.32-3.4) × 10 6 /kg (P = 0.02). The median number mobilizing therapy. 9,10 HDT followed by autologous PBPC of aphereses performed in each group was 5 (4-12) with in MM may induce about 40-60% of complete responses a median of 5.24 ± 2.51 in group I and 3 (2-6) with a in previously untreated patients or in first partial response median of 3.1 (±0.91) in group II (P = NS). Hospitalizafter current induction chemotherapy 1-7,11-13 and some ation for PBPC mobilization was required in all patients investigators have found an advantage regarding response in group I and the treatment-related toxicity was rate, duration of response and progression-free survival greater in this group: 12 patients (66%) developed fever when compared with conventional treatment. 11,12 requiring antibiotics during the neutropenic periodIn spite of the expansion of this strategy, the optimum after HD-CY and six (33%) patients required transsche...