Allogeneic Hematopoietic Stem Cell Transplantation (HSCT) in the Imatinib-Era: Update on the Survival Outcome Following Allogeneic HSCT after Imatinib Failure; Results of the German CML Study IV

Allogeneic HSCT has been established as the only curative treatment option for patients with chronic myeloid leukemia (CML). However, after the advent of tyrosine kinase inhibitors (TKI) the proportion of transplanted patients has decreased dramatically. After imatinib failure, most patients receive second or third line therapy with alternative TKIs. In an important minority of patients, SCT is performed too late as more patients are transplanted after disease progression to accelerated phase or blast crisis than in first chronic phase (CP, Saussele et al. BMT 2012). A possible reason is the uncertainty on long-term outcome after SC T in the imatinib-era as reports are scarce and accurate comparative data on the impact of salvage TKI therapy vs allogeneic transplantation are missing.

We therefore investigated the outcome of transplanted patients within the CML study IV. Preliminary data were published (Saussele et al. BLOOD 2010). Here, we sought to re-evaluate the outcome of these patients with a longer follow-up.

In July 2002, the German CML-Study Group activated a prospective randomized trial comparing different imatinib based strategies in CP CML. Elective early HSCT was considered for patients with EBMT score 0–1 for those with high disease risk, and after imatinib failure.

By the end of March 2012, 1551 patients were randomized. In 2008, HSCT was documented in 84 patients. One patient was not evaluable any more due to withdrawal of consent. 52 patients were male (65%), 23 high risk patients (28%) according to the Euro CML score. Median age at diagnosis was 37 years (range, 16-62), median time to HSCT was 12.6 months (range, 3.5-54). EBMT score was 0-1 in 8 (10%), 2 in 10 (12%), 3-4 in 44 (55%), and >=5 in 18 patients (23%), three patients were missing. Median follow-up after HSCT was 86.9 months (range, 0.3-122). Based on the indication for HSCT three groups are defined: 1) early HSCT, n= 19 (23%; low EBMT score (n=9), high risk patients (n=7), patient request (n=3); 2) HSCT after imatinib failure or intolerance in first CP (n=36 patients, 43%), and 3) HSCT in second CP or higher, accelerated phase or blast crisis (n=28 patients, 34%). 26 patients died, 13 deaths were transplant related, 9 CML related 4 either unrelated or unknown. Overall survival rate at 6 years after HSCT was 89% (95%-confidence interval (CI): 72-99%) for group 1, 80% (95%-CI: 66-91%) for group 2, and 49% (31-68%) for group 3.

A matched pair analysis could be performed for 53 transplanted patients of group 1 and 2. To each of the transplanted patients two imatinib-treated patients could be matched with regard to age, sex, risk profile, disease phase, and interval to transplantation. Median follow up of this population was 87 months. Overall survival after 8 years was 83% (95%-CI: 71-92%) for transplanted and 89% (95%-CI: 82-94%) for imatinib treated patients without any statistical difference.

Data from this update with a longer follow-up support the role of HSCT as an attractive and important salvage therapy for CML patients with imatinib failure or intolerance. In a matched pair comparison of transplanted and non-transplanted patients, we did not find significant differences.