Philadelphia Chromosome Positive Acute Lymphoblastic Leukemia Showing Complete Molecular Response Following Imatinib (Glivec^®) - combined chemotherapy

The Philadelphia (Ph) chromosome is the result of a reciprocal translocation between chromosomes 9 and 22 [t (9; 22)] and is characterized at the molecular level by expression of the BCR-ABL fusion gene. It is the most frequent genetic aberration in adult acute lymphoblastic leukemia (ALL), being detectable in 30–40%of patients with B-precursor ALL. In our initial work we report two cases of grossly negative (Ph) ALL, that showed a complete molecular response after an imatinib based chemotherapy.

In the first case we report a 17-year-old male who was admitted because of bony aches and fever. A diagnosis of acute lymphoblastic leukemia was made on the basis of a 95% infiltration of leukemic cells in his bone marrow. Standard G-banding chromosome analysis of bone marrow cells revealed a normal karyotype. And subsequent fluorescent in situ hybridization (FISH) examination showed a 20% positivity for the Philadelphia chromosome.

As for the second case we report a 19 years old male patient who was presented with complaints of recurrent epistaxis and bony aches. He was also found to have acute lymphoblastic leukemia due to bone marrow infiltration with 55% blasts that showed a normal karyotype using the G- banding, and a positive Philadelphia chromosome-using FISH method - in 31 % of the examined cells.

Both patients received combination chemotherapy incorporating imatinib mesylate; Glivec® in a dose of 400 mg/day continuously all through the induction, consolidation and subsequent re-enforcement courses. They both achieved complete hematological, cytogenetic as well as molecular remission that was maintained-thus far- for a total period of 20 and 11 months respectively. We postulated that there might have been two clones, both a Ph-positive clone and Ph-negative clone, with subsequent sensitivity of this Ph positive clone to the incorporated targeted treatment, as was evidenced by disappearance of the Ph-positive cells in subsequent FISH analysis and the negativity of the real time quantitative polymerase chain reaction (RT-QPCR) for BCR/ABL gene.

Several investigators have studied the role of Hematopoeitic stem cell transplantation (HSCT) in the context of Ph+ ALL patients, which showed superior results when compared to conventional chemotherapy in means of remission induction as well as relapse rates, Dombret et al.2002. The highly successful introduction of the first ABL-kinase inhibitor imatinib into the treatment of Philadelphia chromosome positive chronic myeloid leukemia (CML) has led to clinical testing of imatinib in Ph+ALL. It has recently been approved for Ph+ALL in Europe and Japan. Given the much more aggressive nature of Ph+ALL when compared with chronic or even accelerated phase CML, a variety of imatinib-based treatment strategies have been explored in ALL(Ottman et al.,2007). Yet thus far the exploration of these treatment modalities in the very rare entity of gross normal karyotype and molecular level cytogenetic aberrations remains to be elucidated.

Conclusion: Molecular remission on tyrosine kinase inhibitors in patient with ALL Ph +ve may open the door to revising the treatment strategies offered thus far for that subset of patients, as a new stratifying factor. Our work offers a unique protocol for utilizing imatinib as an integral part of the chemotherapy protocols normally offered for these patients, but yet at a lower dose, and raises the question of whether they should be transplanted in accordance with the current guidelines and if so when? More patients experience and controlled randomized trials are needed and eagerly awaited.