Cytogenetic findings in acute biphenotypic leukaemia.

We have studied the immunological and cytogenetic features of 26 patients with acute leukaemia classified as biphenotypic according to a scoring system based on the number and lineage specificity of antigens expressed on the blast cells. The series included 19 adults (age >15 years) and seven children. The cases were distributed in four immunophenotypic groups: (1)coexpression of myeloid and B antigens, 18 cases (69 percent);(2)myeloid and T cell antigens, six (23 percent); (3) one case with trilineage differentiation; and (4) one case with coexpression of both B and T cell antigens. Cytogenetic analysis revealed a normal karyotype in four cases (15 percent) and abnormal clones in 22 (85 percent). Eight patients had the Philadelphia (Ph) translocation, t(9;22)(q34;q11), (31 percent), three cases had structural aberrations of 6q and two had 11q23 rearrangements, one with t(11;19) and a second with t(4;11); the other eight cases had different alterations including t(9;12)(q1;q1), t(8;21)(q22;q22), t(2;7) (p1?3;q3?4), t(7;12)(q11;p11), hyperdiploidy and other structural abnormalities. The chromosomal rearrangements in children were characterised by abnormalities of 11q23 in two cases and the Ph translocation in three. Our data indicate that biphenotypic features are common in cases presenting with t(9;22) as the eight cases included here represent 47 percent of all cases of Ph+ve acute leukaemia studied in our Institution. Biphenotypic acute leukaemias comprise a heterogeneous group of leukaemias involving pluripotent stem cells. Cytogenetic studies are essential in characterising these cases as they will disclose several poor prognosis chromosome aberrations of which the Ph chromosome is the most frequent.