Relapsed and recurrent acute lymphoblastic leukemia (ALL) remains a major therapeutic challenge for both pediatric and adults.
Relapse occurs in approximately 15–20% of children and the majority of adults with ALL.
Survival rates after relapse significantly lower than at initial diagnosis.
Prognosis is influenced by time to relapse, with early relapse portends worse outcomes, immunophenotype with T-cell ALL is less favorable, and site of relapse-bone marrow involvement is worse than isolated extramedullary relapse.
The primary goal in treating relapsed and recurrent is to achieve a second remission and, when feasible, proceed to allogeneic hematopoietic stem cell transplantation (HSCT), which offers the only curative potential for most patients.
Minimal residual disease (MRD) monitoring is utilized for risk stratification and guiding post-remission therapy.
Treatment Options for B-cell ALL:
Immunotherapies:
Blinatumomab (CD19 BiTE) is indicated for relapsed/refractory B-cell ALL, especially in patients with low disease burden or MRD positivity.
It has demonstrated superior remission rates and overall survival compared to standard chemotherapy, with complete remission (CR) rates of 36–44% and molecular response rates up to 86%.
Inotuzumab ozogamicin (CD22 antibody-drug conjugate) is preferred in patients with higher disease burden.
It achieves higher CR rates (66–81%) but is associated with hepatotoxicity, particularly veno-occlusive disease, and should be avoided in patients with significant liver dysfunction.
CAR T-cell therapy with tisagenlecleuce is approved for children and young adults (≤25 years) with relapsed/refractory B-cell ALL, achieving CR rates of 70–90% and durable remissions in a subset.
CAR T-cell therapy is often used as a bridge to HSCT or as definitive therapy in select patients.
Chemotherapy:
Salvage chemotherapy regimens have limited efficacy, with CR rates of 18–44% and short remission durations.
Allogeneic HSCT:
HSCT remains the standard of care for eligible patients in second remission, offering the highest chance of cure.
Patient selection is based on age, comorbidities, donor availability, and response to salvage therapy.
Philadelphia chromosome-positive (Ph+) ALL: Tyrosine kinase inhibitors (TKIs) are combined with immunotherapies (e.g., blinatumomab, inotuzumab) and/or chemotherapy.
Ponatinib is preferred for T315I mutations.
Blinatumomab and inotuzumab are both effective in relapsed Ph+ ALL
T-cell ALL: Options are more limited; nelarabine is approved for relapsed T-ALL.
CNS relapse: Requires CNS-directed therapy and is an emerging clinical challenge.
Current Challenges and Future Directions:
The choice between blinatumomab, inotuzumab, and CAR T-cell therapy is individualized based on disease burden, prior therapies, age, and comorbidities.
Agents available for relapsed/recurrent ALL include antibody drug conjugates, bIspecific T cell engagers, chimeric antigen receptor T cells, and small molecule inhibitors of apoptosis and tyrosine kinases in biologically defined treatment subsets.
The achievement of minimal residual disease in the front line setting has been shown to be the most favorable prognosticator of treatment outcome and is also associated with improved outcomes following treatment of relapsed disease.
A treatment goal for relapsed/refractory (R/R) ALL is to induce subsequent complete remission and to consolidate it with a human allogeneic hematopoietic stem cell transplant.
In children, relapse outcomes with therapy regimens are associated with duration of initial remission: late relapses of 18 months or greater have a five year overall survival of 78%, whereas those relapsing early in the bone marrow have a five-year overall survival of 11.5%.
In adults relapse outcomes have been worse than in children related to significant toxicity and or relative chemotherapy resistance to agents.