Multiple myeloma (MM) is a recurrent and incurable neoplasm of B-cell origin. MM accounts for about 10% of all hematological malignancies and it is characterized by a clonal proliferation of atypical plasma cells producing monoclonal protein, mostly IgG (1). A median overall survival (OS) was ~ 3-5 years and at least very good partial response (VGPR) rate was 10%, when “older” therapeutic schema e.g. VAD (vincristine, adriamycin, dexamethasone) were used in clinical practice (2). The introduction of novel agents such immunomodulators and proteasome inhibitor resulted in a significant increase of complete remission (CR) rate as well as OS (3, 4, 5). High-dose chemotherapy followed by autologous hematopoietic stem cell transplantation (AHSCT) remains a standard therapeutic procedure for younger MM patients (< 65-70 years) without significant co-morbidities. Particular benefit of AHSCT was observed for patients transplanted in CR after induction chemotherapy (6). A double AHSCT is offered for a small proportion of MM patients, but this procedure is reserved only for patients who did not achieve at least VGPR after a single transplant (7). The safety and efficacy of the 3^rd AHSCT requires further studies due to a low number of patients receiving such procedure so far. Herein, we report on the results of the 3^rd AHSCT for recurrent, chemo-sensitive MM patients.

We retrospectively evaluated the results of AHSCT for MM performed in Department of Hematology and Bone Marrow Transplantation in Katowice in years 2000-2011. Total number of 298 of AHSCT was carried out in 225 MM patients. A single procedure was offered for 225 patients whereas 69 had double AHSCT. Four patients were performed 3 transplants; 2 male and 2 female at a median age of 51 years (range 50-56). The diagnosis of MM was established according to EBMT criteria (8) and disease stage was classified according to Durie-Salmon system (9). Before the transplant, bone marrow examination including immunophenotyping was performed as well as biochemistry and electrophoresis with serum M-protein measurement. All patients gave an informed consent before entering the study. Details of patients characteristics at diagnosis and before 3^rd AHSCT were shown in table 1.

All patients who were proceeded to 3^rd AHSCT received at least 3 lines of chemotherapy. The first-line treatment including VAD regimen was uniform for all patients and they met partial response (PR) criteria before 1^st AHSCT. Two patients converted to CR after 1^st AHSCT and two remained in PR. Due to M-protein increase, all patients received second-line treatment consisting of CTD (cyclophosphamide, thalidomide, dexamethasone; n=3) and VMBCPT (vincristine, melphalan, cyclophosphamide, prednisone, carmustine and thalidomide; n=1). All these patients fulfilled CR criteria before 2^nd AHSCT. The 3^rd transplant was planned as remission consolidation. A median time from diagnosis to 1^st AHSCT was 12.4 months (range 11.6-12.9) and from diagnosis to 3^rd procedure- 42 months (range 42-90). A median time between 1^st and 3^rd AHSCT was 30.5 months (range 27-66). Disease status at the time of AHSCT procedures was presented in table 2.

The source of stem cells was peripheral blood and collection was preceded by IVE regimen (ifosfamide, vepeside, epirubicin). Two patients required an additional stem cell collection preceding by cyclophosphamide before 3^rd AHSCT. Granulocyte-colony stimulating factor (G-CSF) at a dose of 10 ug/kg/day was administered from day +5 to the end of apheresis. The cells were frozen and stored according to standard protocols of our center. Conditioning before AHSCT consisted of melphalan at a dose of 140 mg/m²/d on days 1-2.

Response criteria follow EBMT recommendations (8). Shortly, CR was defined as the absence of M-protein in serum and urine by immunofixation and the presence of less than 5% of plasma cells in bone marrow maintained for ≥ 6 weeks. PR was defined as ≥ 50% decrease of serum M-protein, >90% decrease of light chain (LC) excretion or to < 200 mg in 24h urine collection and ≥ 50% decrease of plasma cells in bone marrow for patients with non-secretory myeloma. Progressive disease (PD) was defined as ≥ 25% increase of serum M-protein, which must also be an absolute increase of ≥ 5 g/L confirmed by repeated study or > 25% increase in LC excretion, which must be absolute increase of ≥ 200 mg/24 h. Stable disease (SD) did not meet CR, PR and PD criteria.

A median number of transplanted CD34+ cells was 6.5 x 10^6/kg (range 3.1-39.2). All patients engrafted. The median time to neutrophil recovery > 0.5 x 10⁹/L was 19 days (range 10-21) and platelet count >50 x 10⁹/L was achieved after median of 14 days (range 14-15). A median time of hospitalization was 25 days (range 20-29). A median number of red blood cells (RBCs) and platelets transfusions was 1 (range 0-2). A median number of intravenous antibiotics administration was 8 days (range 5-10). Transplant-related mortality at day +100 after 3^rd AHSCT was 0%. Two patients remain in CR without maintenance treatment. One patient relapsed 9 months from 3^rd AHSCT, he received subsequent chemotherapy and died due to bilateral pneumonia. The second patient had disease recurrence 4 months from AHSCT. He was treated with TD (thalidomide, dexamethasone) schema and achieved partial response.

High dose chemotherapy followed by AHSCT remains an integral part of MM treatment. AHSCT is offered both as remission consolidation and a salvage procedure in patients with recurrent and resistant MM (10). It seems that the depth of response which has been obtained after induction may influence the long-term outcome after AHSCT. It was reported that AHSCT may increase disease-free survival (DFS) and improve quality of life but it has no impact on overall survival (11). The proportion of MM patients who may achieve CR depends on the presence of the number of adverse prognostic factors as well as the schema used for induction (12, 13). The achievement of at least VGPR after older therapeutic schema was difficult and it was achievable in about 10% of patients (2). Currently, due to novel agents (immunomodulators and proteasome inhibitor) we are witnessing a significant improvement in response rate with about 50% of patients achieving CR (14, 15). Some papers showed that the treatment with bortezomib may result in an increase of DFS and OS in patients with 17p deletion (16). This agent was found to be effective also for patients with t(4;14) (17).

The results of double AHSCT for MM patients are inconclusive. Some studies showed that double AHSCT was associated with an increase of CR and DFS rates if compared with single transplant, but there was no significant difference in terms of OS (18-20). Currently, based on recently published studies, it seems that benefit from double AHSCT is observed especially in MM patients at high risk cytogenetic group (16).

Our paper presents the results of retrospective analysis of 4 patients who underwent 3^rd AHSCT. It should be stressed that our study group did not receive immunomodulators nor proteasome inhibitor in induction treatment and PR was achieved before 1^st AHSCT in all patients. CR was confirmed in 50% of patients after 1^st transplant. 2^nd and 3^rd AHSCT were performed in CR. After median follow-up of 11 months after 3^rd AHSCT and 40.5 months after 1^st AHSCT, 2 patients remain in CR. A median hospitalization time was 25 days and no serious complications were observed. The main drawback of our analysis is the lack of cytogenetic profile at diagnosis which may influence the interpretation of results.

Only single report showing the outcome of 3rd AHSCT was found in the literature. Two MM patients were transplanted due to recurrent disease despite prior AHSCT. After median follow-up of 15 months, they remained in PR (21).

In conclusion, based on our experience and on data from the literature it is difficult to assess the efficacy of 3^rd AHSCT for MM. Doubtless, it is safe procedure, not requiring prolonged stay at hospital. It seems that currently, in the era of new and efficacious agents, this procedure should be reserved only for patients who failed all available conventional treatment. A larger number of patients and longer follow-up is required to assess the efficacy of 3^rd AHSCT.