Acute lymphoblastic leukemia - Survey of immunophenotype, French-American-British classification, frequency of myeloid antigen expression, and karyotypic abnormalities in 210 pediatric and adult cases

Immunophenotypic studies are essential to distinguish acute lymphoblastic l eukemia (ALL)from minimally differentiated acute myeloid leukemia (AML-M0) and to classify ALL into immunologic subtypes, Frequently, immunophenotypin g identifies myeloid antigen expression in ALL, causing a potential diagnos tic problem, To evaluate the immunophenotype of ALL, we studied 210 cases o f pediatric and adult ALL by flow cytometry and compared the results with t he French-American-British (FAB) Cooperative Group classification and the k aryotypic findings. Myeloid-associated antigens were expressed in 78 (45.6% ) of precursor B-cell ALL cases. Pediatric precursor B ALLs had a higher fr equency of myeloid antigen expression than did adult cases. All mature B-ce ll ALL cases were negative for TdT and myeloid antigens. Myeloid antigen ex pression was less frequent in T-cell ALL cases compared with precursor B-ce ll ALL cases. Of the 192 cases submitted for cytogenetic analysis, 147 were abnormal. The most common chromosomal translocation was the Philadelphia c hromosome, which was more likely to have L2 blast morphology and a precurso r B immunophenotype. Myeloid antigen expression was present in 70.8% of Ph- positive cases (P = .008). Chromosome rearrangements involving 11q23 also s howed an increased frequency of myeloid antigen expression. Chromosome tran slocations involving regions of T-cell receptor genes were present in 24% o f T-cell ALL cases. A high percentage of ALL cases however; had various oth er cytogenetic abnormalities, many of which involved less well-studied chro mosomal regions.