Bilineal acute leukemia of B and T lineage with a novel translocation t(9;17)(p11;q11).

We describe a case of bilineal leukemia in a 5-year old boy with a rare immunophenotype and the novel translocation t(9;17)(p11;q11) as the sole chromosomal abnormality. Two immunologically distinct blast cell subsets expressed T-markers (CD2, CD5, CD7) and common ALL markers (TdT, CD19, CD22, CD10), respectively. Both cell populations were CD34 negative. The patient, who presented with CNS leukemia, responded promptly to standard chemotherapy for lymphoblastic leukemia and remains in complete remission 20 months from diagnosis. Other translocations between chromosomes 9 and 17 have been infrequently reported in a variety of leukemias but as yet their biologic significance is unknown. The clinical course of this case suggests that t(9;17)(p11;q11) may not have an adverse influence on the disease outcome. However, the role of t(9;17) in the pathogenesis of this unusual lymphoid phenotype remains unresolved.