Almost all of the Pre-B ALLs have L1 morphology. This stage is defined by the production of cytoplasmic Ig. The presence of a t(1;19) translocation in considered prognostically bad. Both c-ALL and pre-B tend to occur in children between one and ten years of age.
The leukemic cells of patients with pre-B ALL contain cytoplasmic immunoglobulin (cIg), an intermediate stage of B-cell differentiation. Twenty-five percent of patients with pre-B ALL have the t(1;19) translocation.