The flow cytometric pattern of CD34, CD15 and CD13 expression in acute myeloblastic leukemia is highly characteristic of the presence of PML-RAR alpha gene rearrangements

Background and Objective. Rapid identification of AML patients carrying the t(15;17) translocation for treatment decision-making is currently made on the basis of morphologic screening. However, the existence of both false po sitives and negatives highlights the need for more objective methods of scr eening AML cases and further molecular confirmation of the t(15;17) translo cation. Design and Methods. In the present study we analyzed a total of 111 AML cas es in order to investigate whether immunophenotyping based on the assessmen t of multiple-stainings analyzed at flow cytometry could improve the sensit ivity and specifity of morphologic identification of acute promyelocytic le ukemia (APL) carrying the t(15;17) translocation. FISH analysis was used as a complementary technique for cases in which morphology and molecular biol ogy yielded discrepant results. Results. Concordant results between morphology and RT-PCR were found in 102 /111 (91.8%) cases: 34 patients had M-3/PML-RAR alpha(+) and 68 non-M-3/PML -RAR alpha(-) disease. Nine cases showed discrepants results. Multivariate analysis showed that the best combination of immunologic markers for discri minating between M-3/PML-RAR alpha(+) and non-M-3/PML-RAR alpha(-) cases wa s that of the presence of heterogeneous expression of CD13, the existence o f a single major blast cell population, and a characteristic CD34/CD15 phen otypic pattern (p<0.02). A score system based on these parameters was desig ned, and the 34 M-3/PML-RAR alpha(+) cases showed a score of 3 (presence of the 3 phenotypic characteristics). In contrast, only 1 out of the 68 (1.3% ) non-M-3/PML-RAR alpha(-) cases had this score, most of these latter cases (53/68, 78%) scoring either 0 or 1. Therefore, among these cases, immunoph enotyping showed a sensitivity of 100% and a specificity of 99% for predict ing PML/RAR alpha gene rearrangements. Of the 9 cases in which morphology a nd molecular biology results were discrepant, four cases displayed M-3 morp hology without PML/RAR alpha rearrangements by RT-PCR. In only one of these 4 cases did the immunophenotype score 3, this being the only FISH positive case. From the remaining five discrepant cases (non-M-3 morphology while p ositive for PML/RAR alpha) two cases had a phenotypic score of 3 and were F ISH positive while the other three were negative by FISH. Upon repeating RT -PCR studies, two of these latter three cases became negative. Interpretation and Conclusions. Our results show that immunophenotyping may be of great value for quick screening of APL with PML/RAR alpha rearrangem ents. (C)1999, Ferrata Storti Foundation.