Impact of Post-Transplant Cyclophosphamide-Based GVHD Prophylaxis in Patients 70 years and Older: An Update from BMT CTN 1703

• PTCy based GVHD prophylaxis benefit extends to adults ≥ 70 years with improved GVHD control and improved immunosuppression-free survival.

• Overall, the benefit of PTCy translates to lower observed non-relapse mortality and improved overall survival in this older population.

Allogeneic hematopoietic cell transplant (allo-HCT) is underutilized in adults aged ≥ 70 years. Morbidity, often driven by graft-vs-host disease (GVHD), is considered a major barrier to its use. BMT CTN 1703 randomly assigned adults with hematologic malignancies undergoing allo-HCT after reduced intensity conditioning to receive either post-transplant cyclophosphamide, mycophenolate mofetil, and tacrolimus (PTCy) or tacrolimus and methotrexate (Tac/MTX) for GVHD prophylaxis. Overall study results revealed superior GVHD-free, relapse-free survival (GRFS) with PTCy-based prophylaxis. This analysis explored the impact of PTCy in patients ≥ 70 years enrolled to BMT CTN 1703. We analyzed outcomes for 96 patients aged ≥ 70 years. PTCy maintained superiority for the primary endpoint with a GRFS rate of 67.1% compared to 29.5% with Tac/MTX (p=0.001). GVHD control and improved immunosuppression-free survival contributed to a lower 1-year non-relapse mortality (NRM) with PTCy. Further, lower rates of relapse/progression were observed with PTCy, altogether resulting in significantly improved adjusted 1-year survival with PTCy at 94.3% versus 60.2% with Tac/MTX (p=0.001). PTCy based GVHD prophylaxis should be considered standard prophylaxis for older adults. Given low rates of NRM and excellent survival outcomes with this approach, there should be greater consideration for allo-HCT in older patients, particularly patients ≥ 70 years.