Long-Term Survival and Late Events After Allogeneic Stem-Cell Transplantation with Reduced-Intensity Conditioning (RIC) for AML and Mds; Comparable Results with Myeloablative Conditioning.
Authors: Shimoni Avichai , Rand Avital , Shem-Tov Noga , Hardan Izhar , Volchek Yulia , Maayaan Hannah , Yerushalmi Ronit , Nagler Arnon 
Published: October 2019

Abstract
Abstract 518
Allogeneic stem cell transplantation (SCT) is a potentially curative therapy for patients (pts) with AML and MDS. SCT is associated with substantial mortality during the first 2 years after treatment due to relapse and non-relapse causes, whereas after 2 years survival curves often reach a plateau. However, late mortality and late events continue to cause treatment failures through the late post-transplant course. The pattern of late events has been reported following myeloablative conditioning (MAC) but is not well defined in the RIC setting. To explore late outcomes we retrospectively analyzed SCT results in a cohort of 298 pts with AML/MDS given allogeneic SCT with various regimens. As a general role, pts meeting standard eligibility criteria were given MAC, consisting of high dose intravenous busulfan (Bu) and cyclophosphamide (BuCy). Pts considered at excessive risk for non-relapse mortality (NRM), mostly due to advanced age, were given a reduced toxicity regimen such as fludarabine with high-dose Bu (FB4) or treosulfan (FT) or a RIC regimen of fludarabine and reduced doses of Bu (FB2). The 2-year and 5-year overall survival (OS) for this cohort was 48% (95CI, 42-54) and 38% (95CI, 31-44), respectively. We identified 93 pts who were alive and leukemia-free 2 years after SCT. The median age at SCT was 52 years (17-72), 52 male, 41 female. The donors were HLA-matched siblings (n=57) or unrelated donors (n=36. The conditioning regimen was FB2 (n=28), FB4 (n=21, FT (n=15) or BuCy (n=29). At the 2-year time-point, 28 pts had a history of acute GVHD, 68 had a history of chronic GVHD, 43 had active chronic GVHD which still required immune suppressive therapy (IST) in 37. Among pts surviving leukemia-free 2 years after SCT, the probability of remaining alive and leukemia-free, for the next 5 years, was 81% (95CI, 71-91) and 79% (95CI, 69-88), respectively. The probability of OS was 75%, 84%, 92% and 79%, after the various regimens, respectively (p=NS). There were 14 deaths beyond 2 years, 8 deaths due to relapse and 6 due to NRM. NRM included 3 deaths due to solid cancers, 2 due to breast cancer (both in pts transplanted for therapy related AML relapsing with the primary malignancy) and one due to colon cancer. There were 3 additional secondary cancers; breast cancer, squamous cell skin cancer and Kaposi sarcoma (1 pt each; all currently alive). Two pts died of myocardial infarction and one of chronic GVHD. In all, the cumulative incidence of late NRM was 10% (4-24). Interestingly, unlike the early post-transplant period, with current supportive care regimens, late deaths from GVHD and infections are rare. Twelve pts relapsed, 24-59 months after SCT, cumulative incidence 12% (6-23); 8 died, 4 are alive following further therapies, 3 long-term. The kinetics of late relapses was similar with MAC and RIC. Advanced age (&gt;50) was the most significant predicting factor for shortened survival. OS was 64% and 92%, in the older and younger groups, respectively (p=0.03). All deaths due to NRM, and all secondary cancers occurred in the older group (p=0.01). Multivariate analysis (MVA) identified advanced age as the only independent predicting factor for OS; HR 3.1 (1-11.3). The conditioning regimen, disease status at SCT and donor type were not predictive. A history of acute or chronic GVHD predicted improved leukemia-free survival. Age was the most important predicting factor for NRM Active chronic GVHD was the most important factor predicting for reduced relapse risk. The cumulative probability of stopping IST by 7 years post SCT, for the entire cohort, was 73% (63-82). This probability was related to the conditioning regimen and was 80%,76%,80% and 63%, after FB2,FB4,FT and BuCy, respectively (p=0.06 for BuCy versus others). MVA identified conditioning with BuCy (HR 1.8, p=0.06) and male gender (HR 1.7, p=0.04) as predicting for prolonged need for IST. Among the 37 pts who were still on IST 2 years after SCT, the cumulative probability of stopping IST during the following 5 years was only 35%. It was higher in younger pts (59% Vs 15%, p=0.05) and in pts given FB2 (42% Vs. 31%, p=NS). In conclusion the pattern of late outcome is similar after MAC and RIC. Younger pts with AML/MDS who are leukemia-free 2 years after SCT can expect a very good outcome, while older pts are at higher risk for NRM and second cancers, which may not always relate directly to SCT. Pts given RIC are more likely to be able to stop IST, which may be associated with a better quality of life.

Disclosures:
No relevant conflicts of interest to declare.