Impact of pre-transplant induction cycles on post-transplant outcomes in patients with ALL: a study from the ALWP EBMT.

The impact of the number of induction cycles required to achieve first complete remission (CR1) on transplant outcomes in adult acute lymphoblastic leukemia (ALL) patients remains unknown. We conducted a retrospective EBMT registry analysis (2000-2022) of ALL patients who underwent transplantation in CR1 after one (n = 2038), two (n = 296), or three or more (n = 110) induction cycles. Median age was 40 years (range 18-73); 79% had B-ALL. At 2 years, relapse incidence was 23%, 31%, and 32%, while non-relapse mortality was 17%, 18%, and 16%, for those achieving CR1 after one, two, and ≥3 cycles, respectively. Multivariable analysis showed that requiring ≥2 cycles was associated with increased relapse risk. Leukemia-free survival (LFS) at 2 years was 60%, 51%, and 52%, and overall survival (OS) was 68%, 61%, and 60%, for patients needing one, two, and ≥3 cycles, respectively. Multivariable analysis confirmed significantly worse LFS and OS in patients requiring multiple cycles versus one. These findings suggest that the number of induction cycles to achieve CR1 is a key prognostic factor for post-transplant outcomes in adult ALL and support the development of risk-adapted strategies in this setting.