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.
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