MRD at the End of Induction and EFS in T-cell Lymphoblastic Lymphoma: Children's Oncology Group Trial AALL1231

• The level of MRD in the bone marrow at the end of induction correlates with event free survival in T cell lymphoblastic lymphoma.

• MRD at the end of induction may be a prognostic variable for event free survival in pediatric T cell lymphoblastic lymphoma

Defining prognostic variables in T-lymphoblastic lymphoma (T-LL) remains a challenge. AALL1231 was a COG phase 3 clinical trial for newly diagnosed with T Acute Lymphoblastic leukemia or T-LL patients randomizing children and young adults to a modified augmented BFM backbone to receive standard therapy (Arm A) or with addition of bortezomib (Arm B). Optional bone marrow (BM) samples to assess minimal residual disease (MRD) at the end of induction (EOI) were collected in T-LL analyzed to assess the correlation of MRD at the EOI to event-free survival (EFS). Eighty-six (41%) of the 209 T-LL patients accrued to this trial submitted samples for MRD assessment. Patients with MRD <0.1% (n= 75) at EOI had a superior 4-year EFS versus those with MRD >0.1% (n= 11), (89.0±4.4% versus 63.6±17.2%, p= 0.025). Overall survival did not significantly differ between the two groups. Cox regression for EFS using Arm A as a reference demonstrated that MRD EOI ≥0.1% was associated with a greater risk of inferior outcome (Hazard Ratio, HR= 3.73 (1.12-12.40, p= 0.032), which was independent of treatment arm assignment. Consideration to incorporate MRD at EOI into future trials will help establish its value in defining risk groups. CT# NCT02112916