Incidence of extramedullary relapse after haploidentical SCT for advanced AML/myelodysplastic syndrome

Extramedullary (EM) relapse of leukemia after allo-SCT in patients with AML/myelodysplastic syndrome has been increasingly reported. The reduced effectiveness of the GVL effect in EM sites, as compared with BM, has been suggested to underlie this problem. We retrospectively analyzed the pattern of relapse after haploidentical SCT (haplo-SCT), performed as the first or second SCT. Among 38 patients who received haplo-SCT as their first SCT, the cumulative incidences of BM and EM relapse at 3 years were 40.5 and 10.9%, respectively. Among 19 patients who received haplo-SCT as their second SCT, the cumulative incidences of BM and EM relapse were 30.9 and 31.9%, respectively. Moreover, most of the patients who underwent repeat haplo-SCT for the treatment of EM relapse had further EM relapse at other sites. Post-relapse survival did not differ significantly with different patterns of relapse. The frequent occurrence of EM relapse after haplo-SCT, particularly when performed as a second SCT, suggests that the potent GVL effect elicited by an HLA disparity also occurs preferentially in BM. Our findings emphasize the need for a treatment strategy for EM relapse that recognizes the reduced susceptibility of EM relapse to the GVL effect.