Randomized phase 3 trial of iodine-131 apamistamab before alloHCT for relapsed or refractory AML in older patients

Older patients with relapsed or refractory (R/R) AML have dismal prognoses without allogeneic hematopoietic cell transplantation (alloHCT). The multicenter phase 3 SIERRA trial in the USA evaluated a targeted pretransplant regimen involving the anti-CD45 radioconjugate ¹³¹I-apamistamab for R/R AML in patients aged 55 years or older. Patients were randomized 1:1 to ¹³¹I-apamistamab or usual care (UC) before alloHCT; patients without CR/CRp or with AML progression could cross over to receive ¹³¹I-apamistamab. The primary endpoint was durable complete remission (dCR) lasting 180 days after initial CR/CRp. The dCR rate was 17.1% with ¹³¹I-apamistamab versus 0% with UC. The event-free survival HR was 0.23 (95 CI 0.15-0.34) favoring ¹³¹I-apamistamab. Grade 3 or higher treatment-related adverse events were reported for 59.7% and 59.2% of both groups. The authors conclude that the pretransplant ¹³¹I-apamistamab regimen was associated with a higher dCR rate than UC in older patients with R/R AML. The regimen was well tolerated and could address an unmet need in this population.