The long-term impact of in vitro drug sensitivity on risk stratification and treatment outcome in acute lymphoblastic leukemia of childhood (CoALL 06-97)

Background In a study of childhood acute lymphoblastic leukemia (CoALL 06-97 study), the in vitro sensitivity of the patients' cells to prednisolone, vincristine and asparaginase was introduced as a new additional risk parameter for treatment stratification. In parallel in vivo treatment response was assessed by determining the presence and extent of minimal residual disease in a subset of patients (n=224). Here we report the long-term impact of in vitro sensitivity-based risk stratification according to survival and compare the results of in vitro sensitivity with in vivo response. Design and Methods Patients with a sensitive in vitro profile were treated with a reduced intensity protocol (n=167) whereas patients defined as low risk according to conventional parameters but with a resistant in vitro profile were given intensified therapy (n=47). Results At a median follow-up of 6.8 years event-free survival was 0.80 +/- 0.03 for patients with a sensitive profile, 0.73 +/- 0.03 for those with an intermediate profile and 0.67 +/- 0.08 for those with a resistant profile (P=0.015). Overall, the treatment results of the cases stratified according to in vitro sensitivity were similar to those of the historical control group stratified based on conventional risk factors. Minimal residual disease at the end of induction was a strong predictor of outcome in B-precursor and T-cell acute lymphoblastic leukemia. There was no correlation between in vitro and in vivo treatment response in B-precursor leukemia (Spearman's r=0.13; P=0.15) in contrast to T-cell acute lymphoblastic leukemia (Spearman's r=0.63; P<0.001) Conclusions A moderate reduction in treatment intensity for patients with a sensitive in vitro profile was possible without jeopardizing treatment outcome. However, in vitro drug testing was affected by a decrease in risk predictive power over time and was not correlated with in vivo assessment of minimal residual disease in B-precursor acute lymphoblastic leukemia. It was, therefore, abandoned in favor of the assessment of in vivo response in subsequent CoALL trials.