Application of Multiplex RT-PCR for Identification of Leukemia Associated Gene Abnormalities.

The best prognostic predictor for acute leukemia is known to be the finding of genetic abnormalities of leukemic cells. Methods for detecting the genetic abnormalities include chromosomal studies for karyotyping, FISH(Fluorescence in situ hybridization) and RT-PCR. However, each methods have limitations i.e. low sensitivity in karyotyping, uncertainty of molecular probe to be used in FISH or RT PCR methods. Multiplex RT-PCR (MRT-PCR) allows simultaneous detection of 28 fusion genes, more than 80 breakpoints and splice variants associated with leukemia. Therefore, this method can be used for detection of molecular abnormality in fresh unknown leukemic cases, as well as for molecular remission in follow-up cases. The aim was to demonstrate whether MRT-PCR system might be successfully used to screen a large number of patients with acute leukemia and compare the result with that of chromosome studies. Frozen bone marrow cells from 78 patients, who were diagnosed with acute leukemia at Ajou university hospital between September 1994 and February 2004, were used for MRT-PCR. In all samples with a known conventional cytogenetic results, we performed MRT-PCR and to compared with conventional cytogenetic study regarding the concordance rate and analyzed discordant cases regarding their types. 78 samples(40 male and 38 female patients) were analyzed, and there were 59 AML patients and 19 ALL patients. We successfully obtained the mRNA from all frozen samples. In 21 cases with gene abnormalities by chromosome studies most of them (15/21) showed the same abnormalities with MRT-PCR. In 57 patients with normal karyotype by cytogenetic technique, we identified 18 translocations of clinical significance by MRT-PCR method. In 18 discordant cases, there were 4 cases with t(15;17), 4 cases with t(8;21), 3 cases with t(9;22), 2 cases with t(11;19) and 4 others [t(9;11),t(9;9),t(3;11),inv(16)]. Conventional cytogenetics detected 10 cases of good prognostic gene abnormalities [t(15;17),t(8;21),inv(16)], but MRT-PCR method detected 10 additional cases of good prognostic gene abnormalities which might change the treatment paln. The twenty good prognostic cases with MRT-PCR showed better overall survival than others. (median f/u = 10.6 month, p=0.0443) There were 69% concordance rate between cytogenetic technique and MRT-PCR. Furthermore clinically significant translocations were detected by MRT-PCR in 18 of 57 normal karyotype patients, indicating improved sensitivity and prognostic value with MRT-PCR. Further investigations are needed to ascertain the usefulness of MRT-PCR for the screening tool of leukemic gene abnormalities.