Purpose: Despite improvements in treatment, approximately 20% of patients with acute lymphoblastic leukemia (ALL) experience relapse and do poorly. The Therapeutic Advances in Childhood Leukemia (TACL) Consortium was assembled to assess novel drugs for children with resistant leukemia. We hypothesize that novel agents and combinations that fail to improve baseline complete remission rates in comparable populations are unlikely to contribute to better outcomes and should be abandoned. We sought to define response rates and disease-free survival (DFS) rates in patients treated at TACL institutions, which could serve as a comparator for future studies.

Patients and Methods: We performed a retrospective cohort review of patients with relapsed and refractory ALL previously treated at TACL institutions between the years of 1995 and 2004. Data regarding initial and relapsed disease characteristics, disease response, and survival were collected and compared with those of published reports.

Results: Complete remission (CR) rates (mean ± SE) were 83% ± 4% for early first marrow relapse, 93% ± 3% for late first marrow relapse, 44% ± 5% for second marrow relapse, and 27% ± 6% for third marrow relapse. Five-year DFS rates in CR2 and CR3 were 27% ± 4% and 15% ± 7% respectively.

Conclusion: We generally confirm a 40% CR rate for second and subsequent relapse, but our remission rate for early first relapse seems better than that reported in the literature (83% v approximately 70%). Our data may allow useful modeling of an expected remission rate for any population of patients who experience relapse.