Durability of response after horse ATG. (A) Time to first late event among responders. The probability of a first late event (relapse or clonal evolution) among responders (N = 243) is approximately 50%. (B) In those who do not experience a late event, long-term survival in 10 years is excellent at 95%, whereas in those who experience a late event survival is not as favorable (65% in 10 years). (C) In our experience, high-risk evolution to monosomy 7, complex karyotype, high-grade myelodysplasia, or leukemia occurs in approximately 10% of responders long term. (D) Among responders who clonally evolved (any cytogenetic abnormality), survival was worse in those with a high-risk clonal event (monosomy 7, high-grade myelodysplasia, complex karyotype, or leukemia) compared with responders who do not experience high-risk evolution (principal karyotype findings in this lower risk group were trisomy 8 and del13q). Of note, among the high-risk clonal evolutions in responders, all occurred in those who achieved a partial hematologic response at 6 months after immunosuppression. (A,C) SD values (P = log-rank). Day 0 for all curves is the time of first horse ATG-based therapy. Data for other experimental immunosuppressive therapies as first-line are not shown. A late event is defined as either relapse or clonal evolution, whichever occurred first. Patients with repeated relapses or cytogenetic abnormalities were counted once at the time of first event.