Case examples from gilteritinib arm. MRD, relapse, and drug exposures are displayed for 6 participants randomized to gilteritinib. Note that all investigators and participants were blinded to both study drug and MRD status. The colored thin lines represent the FLT3-ITD MRD clones and the thick black bars depict the periods when the participant was being treated with gilteritinib. Pt (participant) 1: 3 clones (21, 30, 45 base pairs [bp]) detected before and after HCT. Started gilteritinib on post-HCT day +41, maintained continuously on 120 mg/d for 24 months. The 30-bp clone was not detected at 2 time points, then rose steadily until 24 months after HCT. Gilteritinib was stopped per protocol, with the pt still in morphologic remission, and the pt relapsed 6 weeks later. Pt 2: single 30-bp clone detected before and after HCT. Started gilteritinib on post-HCT day 43. Clone eradicated, but pt relapsed 8 months after HCT with AML confirmed by PCR/capillary electrophoresis to be wild-type FLT3. Pt 3: single 54-bp clone detected both before and after HCT. Started gilteritinib on post-HCT day 35, with concomitant posaconazole. Lactate dehydrogenase was elevated to grade 3 and gilteritinib was decreased briefly to 80 mg/d, and then discontinued permanently on day +51. Relapsed on post-HCT day 134. Pt 4: single 42-bp clone detected before and after HCT. Started gilteritinib on post-HCT day 86, maintained continuously for 24 months, then stopped per protocol. The 42-bp clone was detected throughout, slowly decreasing in level. Pt alive and relapse free 49 months after HCT. Pt 5: 5 clones detected before HCT, all negative immediately after HCT. A new 159-bp clone appeared after HCT, before randomization. Started gilteritinib with concomitant itraconazole, but the gilteritinib had to be held twice for thrombocytopenia and resumed at 80 mg/d, with a resultant gilteritinib trough level of only 77.5 ng/mL (which is approximately one-third the median trough level for all other participants¹⁷). The 159-bp clone became undetectable, but the 21-bp clone that had been detected before HCT reappeared on post-HCT day 142. Pt relapsed with the 21-bp and the 57-bp clone while on 80 mg/d gilteritinib. Pt 6: 2 clones detected before HCT, and a 63-bp clone persisted after HCT. Started gilteritinib on post-HCT day 50 and posaconazole started prophylactically on day post-HCT day 70. The absolute neutrophil count dropped to 100/mm³ on post-HCT day 105 and gilteritinib was stopped. Gilteritinib was resumed on post-HCT day 131 (again with concomitant posaconazole), but the neutrophil count decreased again and the study drug was permanently stopped on post-HCT day 138. Pt relapsed 2 months later with the 63-bp clone.