About half of B-cell precursor ALL cases in pediatric patients have positive CD20 expression, and, as shown by some studies, up-regulation is frequent throughout classic chemotherapy regimens, especially due to corticosteroid use which plays a role in ALL blast differentiation toward mature B-cells as demonstrated by down-regulation of CD10 and CD34, and up-regulation of CD20 [8,9,10,11,12]. Here, CD34 is linked to acute lymphoblastic leukemia.