Long Term Outcome After Low Dose TBI Based Conditioning Hematopoietic Stem Cell Transplantation (HSCT) From Related and Unrelated Donors for Older Patients with AML
Authors: Niederwieser Dietger , Verdonck Leo F , Cornelissen Jan J , Cross Michael , Krahl Rainer , Lange Thoralf , Vucinic Vladan , Franke Georg , Al-Ali Haifa K. , Ossenkoppele Gert , Maschmeyer Georg , Doelken Gottfried , Freund Mathias , Peter Norma , Boogaerts Marc , Gratwohl Alois , Schouten Harry C. , Lowenberg Bob 
Published: October 2019

Abstract
Abstract 2030
HSCT after reduced or minimal intensity conditioning is increasingly used to treat AML patients not eligible for conventional HSCT. Short term outcome has been reported frequently and risk factors have been identified; long term results still await in depth evaluation. We report here 5 years follow up results from a prospective phase II study conducted by two AML study groups in Europe.
Patients were recruited from AML protocols HOVON/SAKK AML 43 and the OSHO AML 1997 study. The regimen consisted of fludarabine (FLU), 30 mg/m2/d on days −4, −3, and −2, 2 Gy TBI on day 0 (the day of HSCT) with mycophenolate mofetil, [15 mg/kg p.o. b.i.d. from 5 hours after HSCT to day +40], and cyclosporine, [CSP; 6.25 mg/kg p.o. bid from day –3 to day +180] after HSCT. Cyclosporine was adjusted to trough levels and reduced according to a predetermined tapering schedule and donor type.
A total of 96 patients were recruited between 5/2002 and 8/2005 in the study. Age was median 62 (range 40 – 74) years, 54 patients were male (56%) and 73 patients (76%) had de novo AML. The remission status on entry was CR1 in 83 (86%) patients and CR2 in 13 (14%). Of the 96 patients, 20% had high risk cytogenetics and SCT was performed a median of 75 days after chemotherapy. There were no statistical differences in the above described characteristics except for more secondary AML (p=0.04) and more CR2 patients (p=0.07) among the 59 unrelated SCT (61%) as compared to the 37 related SCT (39%). Graft rejection at two years was observed in 6% of the patients. Absence of chronic GvHD was diagnosed in 40% and limited chronic GvHD in 29% of the patients, with no difference between related and unrelated SCT.
Probability of overall survival (OS) at 6 years with a median follow up of 64 (49–92) months reaches a plateau after 5 years at 0.33±0.05 and was not significantly better in CR1 than in CR2. However, there was a trend towards better OS at 6 years for unrelated 0.41±0.11 as compared to related 0.29±0.07 SCT (p=0.08) in CR1 only. This difference was significant for disease free survival (DFS) (0.48±0.09 unrelated vs 0.27±0.06 related; p=0.04), the major reason being a higher relapse rate in related as compared to unrelated SCT (0.62±0.08 vs 0.40±0.09). The overall non-relapse mortality at 6 years was 0.21±0.05.
We conclude that OS and DFS reach a stable plateau from 5 years after SCT to more than 8 years after SCT. In CR1 patients, DFS is superior after unrelated as compared to related SCT. Accordingly, strategies designed to decrease relapse, especially after related SCT, have already been implemented in the ongoing protocols. The preferential use of unrelated rather than related donors may be beneficial and should be considered in future protocols.

Disclosures:
Off Label Use: Transplantation in elderly patients.