Allogeneic Hematopoietic Stem Cell Transplantation Overcomes the Adverse Prognostic Impact of CD20 Expression In Both Adult and Pediatric Acute Lymphoblastic Leukemia

Abstract 1681 The heterogeneous expression of CD20 antigen on leukemic blasts may harbor prognostic value and therapeutic potential. CD20 positivity (CD20+) has been recently associated with disease recurrence and shorter overall survival in adults with pre-B acute lymphoblastic leukemia (ALL). The influence of CD20 expression on outcomes following allogeneic donor hematopoietic stem cell transplantation (HCT) is not known. Results: We analyzed CD20 expression on pre-B ALL marrow blasts at diagnosis in 157 consecutive patients who underwent allogeneic HCT in first or second complete remission (CR) from 1999–2010. Thirty-two patients with no available flow cytometry data were excluded. Out of 125 evaluable patients, 52 (42%) were < 20 years of age; 73 (58%) were ≥20. All patients had high risk ALL and were in CR at HCT (57% in CR1, 43% in CR2). A majority of patients were Ph+ (60%) and received myeloablative conditioning (84%). Grafts were from sibling (36%), unrelated umbilical cord blood (UCB) (59%) and matched adult URD (5%). CD20+, defined as >20% expression on marrow blasts, was observed in 58 (46%) patients. 55% of children and 39% of adults were CD20+ and expression was similar in CR1 & CR2. Gender, donor source (sibling vs UCB), patient CMV serostatus, cytogenetics (Ph+ vs other), and conditioning (myeloablative vs reduced intensity) was similar in CD20+ and CD20- groups. Disease-free survival (DFS) at 3 years was 48% (95% CI 39–57%) for all patients; 42% (95% CI 30–54%) for CD20- patients, and 55% (95% CI 40–67%) for CD20+ patients (p=0.14). CD20+ expression did not significantly impact relapse rate or DFS in adults (Table) while in patients Conclusion: Pre-B ALL with a CD20+ immunophenotype reportedly confers higher risk of disease recurrence and unfavorable OS with conventional chemotherapy. Our data demonstrates that the poor prognosis associated with CD20+ ALL blasts is overcome by allogeneic HCT. In addition, post-HCT survival is promising in both adults and children, independent of CD20 expression. CD20 targeting monoclonal antibodies may further improve these outcomes. Disclosures: No relevant conflicts of interest to declare.