Frequency of p190 and p210 BCR-ABL Fusions Genes in Acute Lymphoblastic Leukemia in a Long Group of Adults and Childhood

The Ph chromosome is a translocation (9;22)(q34;q11), that results in the constitutive activation of the BCR/ABL tyrosine kinase. The incidence of BCR/ABL in Acute Lymphoblastic Leukemia (ALL) increases with age, from less than 5% in younger children to 20-30% in older adults, with a peak incidence in patients aged 35-50 years. BCR/ABL1 has diverse breakpoints, in adult patients with Ph+ ALL the p190BCR/ABL transcript e1a2/e3a2 may be documented in 50-70%; p210BCR/ABL b2a2/b3a2 in 15-30% of patients and <1% having both breakpoint. Childhood patients with Ph+ ALL fusion genes present p190BCR/ABL transcipt e1a2/e3a2 in 90% and the remaining present other fusion transcrit or co-expression of both p190 and p210 BCR-ABL.

OBJETIVE. The aim of this study was identify the occurrence of fusion genes to p190 and p210 BCR-ABL rearrangements in adult and childhood patients with ALL.

METHODS. We include between 2008-2015 870 patients with ALL de novo from seven different hospitals from México, the 45% (394) were childood and the rest 55% (476) were adults. All patients were studied to RT-PCR multiplex and nested in RNA for fusion transcripts 190 and p210 BCR-ABL, at diagnosis, according to the international BIOMED-1 protocol.

RESULTS. From 870 patients with ALL, the most frequent subtype FAB were L2 (87%) and second L1 (13%). The immunophenotype by B-ALL was to 80%, bilineal in 5% and the rest have not data.

The overall incidence to BCR-ABL in both children and adults with ALL were to 17% [147/870]. The analysis by age group were; in 476 adults with ALL, their average age was 37 years old (range 17-84 years) and their incidence of BCR-ABL positive was 20% (95/476 cases). The distributions by type of fusion transcript were 83% p190 and 17% p210; we did not observe co-expression of transcripts to BCR-ABL. In children patients the average age was 9 years old (range 0.1-16 years), the incidence of BCR-ABL was 13.2% (52/394 cases). The distributions by type of fusion transcript to BCR-ABL were p190 78.8%; p210 13.4% and their co-expression by both isoforms 8%.

CONCLUSION. The 20% frequency for BCR-ABL1 in adults with ALL is concordant with others reports published, with values from 17% to 37% with predominancy of p190 (83%). In our pediatric patients group with ALL, document a frequency of 13.2% by BCR-ABL1 positive; it is higher than other populations reporting 5-10%. The distributions of fusion transcript p190 and p210 coincides with previous prevalence estimates in other countries where p190 transcript was the most frequent. But the coexpression of both isoforms [p190/p210] were 8% it has not been reported in this age group with ALL.

In conclusion, we recommend to identify the BCR-ABL transcript type in every patients with ALL at diagnosis, using a RT-PCR verified method for P190/p210 and followed the patient by mesure the impact clinical and will be adjust the treatment like o plus the cytogenetic studies.