Excellent prognosis of late relapses of ETV 6 / RUNX 1-positive childhood acute lymphoblastic leukemia : lessons from the FRALLE 93 protocol Running title : Prognosis of ETV 6 / RUNX 1 leukemia relapses

Background. The prognosis of relapses of ETV6/RUNX1-positive acute lymphoblastic leukemia remains to be evaluated, particularly with regards to the frequency of late relapses. We performed a long term follow-up a retrospective study to address the outcome of ETV6/RUNX1-positive leukemia relapses. Design and Methods. Among the 713 children tested for ETV6/RUNX1 enrolled into the FRALLE 93 protocol, 43 ETV6/RUNX1-positive patients relapsed (19.4%). Most were initially stratified as low or intermediate risk groups. Median follow-up after relapse was 54.2 months. All but three received a second-line salvage therapy and 16 underwent an allogeneic transplantation. Results. ETV6/RUNX1 greatly impacted on overall survival after relapse (3 year-survival= 64.7 % for positive versus 46.5 % for negative cases) (p= 0.007). The 5-year cumulative incidence of relapse was 19.4% and testes were more frequently involved in ETV6/RUNX1-positive relapses (p=0.04). 81.4 % were late relapses, early combined or isolated extramedullar relapses. The 5-year survival rate of ETV6-RUNX1-positive acute lymphoblastic leukemia relapses reached 80.8% when relapse occurred after 36 months (vs 31.2%). In univariate analysis, female gender was associated with a poor survival, whereas site of relapse, age at diagnosis, leukocytosis and consolidation strategy had no effect. In multivariate analysis, only the duration of first remission remained associated with outcome. Conclusions. We found an excellent outcome for ETV6/RUNX1-positive leukemia relapses occurring over 36 months post-diagnosis. Duration of first complete remission may thus be a guide to define the treatment strategy of ETV6/RUNX1-positive leukemia relapse. DOI: 10.3324/haematol.2011.059584