Koh et al. Journal of Experimental & Clinical Cancer Research 2011, 30:36 http://www.jeccr.com/content/30/1/36 Page 6 of 7 Figure 4 Kaplan-Meier estimates of overall survival based on a landmark analysis at 6 months post-transplant, grouping patients according to primary or secondary leukemia and prior history of cGVHD (p = .060). The 5-year survival rates of patients with primary & prior history of cGVHD + and primary & prior history of cGVHD - were 64% and 25%, respectively. show that this sequential regimen had an advantage in controlling active leukemia. However, we speculated that effective tumor reduction by individual chemother- apy and/or conditioning for allo-HCT to control disease until cGVHD subsequently occurred might also be important, particularly in rapidly proliferating leukemia. In contrast, intensive conditioning did not appear to be essential in relatively indolent leukemia, even with non- remission. Based on our results, CB might be unsuitable as a source of stem cells for treatment of active leukemia at the time of allo-HCT. However, most patients receiving CBT could not wait for an unrelated donor search because their disease tended to be aggressive compared with those in the unrelated BM group. Thus, it is diffi- cult to arrive at any conclusions about the best stem cell source for allo-HCT in patients in non-remission status based solely on our results. Our study has several limitations. The results might be affected by an underlying selection bias due to the nat- ure of retrospective data. Also, our study was limited by the small number of patients, the heterogeneity of the disease, the transplant procedure and the stem cell source. However, the major strengths of our study were that the follow-up period was sufficient with more than 5 years and the impact of cGVHD as well as pre-transplant factors on long-term survival were ana- lyzed exclusively for subjects with active leukemia. Conclusion These data show that allo-HCT has the potential to cure active leukemia possibly via cGVHD, particularly in patients with favorable factors even when in non-remis- sion. Further research is warranted to explore the essen- tial factors contributing to the success of allo-HCT such as intensity of conditioning, and GVL effects mediated through cGVHD. Acknowledgements This work was supported by a Grant-in-Aid for Scientific Research from the Japanese Ministry of Education, Science, Sports, and Culture, and a grant from the Japanese Ministry of Health, Welfare, and Labour. 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