PCR-detectable transcripts in long-term remission of P190^BCR/ABL-positive acute lymphoblastic leukemia

During the past decade, we monitored longitudinally by reverse transcriptase polymerase chain reaction (RT-PCR) 22 adult patients with Ph1-positive and BCR/ABL-positive acute lymphoblastic leukemia (ALL) who were not eligible for allogeneic bone marrow transplantation (BMT). Although like other investigators1we found that PCR-positivity during remission was associated with poor outcome in the whole population (data not shown), we observed prolonged persistence of PCR-detectable minimal residual disease (MRD) in 2 P190^BCR/ABL-positive patients who remained in long-term hematologic complete remission (HCR). The main presenting features, type of treatment, and clinical and molecular outcome of these 2 patients are reported in Table1. Patients received induction chemotherapy (CHT) according to the GIMEMA ALL-0288 and ALL-0394 protocols,2,3 respectively. As postremission therapy, patient 1 (diagnosed in 1989) was treated with CHT alone, including intensive consolidation and 2-year conventional maintenance.2 In addition, due to hepatitis C virus (HCV) infection diagnosed in 1997 while off therapy for 6 years, he received 1 year's treatment with interferon alpha (IFN-α). He remains presently in continuous PCR-positive HCR after more than 114 months from HCR achievement. Patient 2 underwent, after CHT consolidation, early autologous stem cell transplantation (ASCT), followed by 1 year's maintenance with IFN-α according to the European Intergroup trial for Ph1-positive adult ALL.4 She remained in HCR and persistently PCR-positive for 52 months, at which point hematologic relapse was documented. The patient died of disease progression 3 months later. Persistence of P190 BCR/ABL transcripts was detected in all sequential marrow specimens collected at 3-to-6-month intervals from the 2 patients. The sensitivity of the employed RT-PCR assay ranged between 10^-4 and 10^-5, as reported elsewhere.5 The following precautions were undertaken to avoid contamination: (i) RNA extraction and RT-PCR analyses were always performed in separate rooms; (ii) plugged aerosol-resistant pipettes were used at all stages; and (iii) a negative control (all reagents plus water with no template) was included in each experiment. Finally, 2 bone marrow samples were processed for RNA extraction and analysed by RT-PCR in an another laboratory using the same assay, and positivity was confirmed in both cases. Diagnostic and some of the follow-up RNA samples still available were reanalysed recently by the real-time quantitative PCR (Q-PCR) using the Taqman ABI Prism 7700 Sequence Detector (Perkin-Elmer Applied ByoSystem, Foster City, CA). In patient 2, a 2 log-decrease of the P190^BCR/ABL transcripts, as compared to diagnosis, was detected after consolidation with ASCT. Such level remained stable for the next 12 months during IFN-α maintenance and for the successive 21 months after IFN discontinuation. In a subsequent sample collected 6 month later (6 months before hematologic relapse), a significant increase of the hybrid mRNA level was detected. In patient 1, only 2 sequential samples taken during IFN maintenance were available. Hybrid mRNA molecules levels were 2 logs below the diagnostic level.

PCR-positivity in long-term HCR has been reported very recently in 2 of 5 BCR/ABL-positive ALL patients receiving IFN-α maintenance for longer than 2 years.6 The significance of persistent MRD in patients in both that study and our study is presently unclear. Although a beneficial effect of IFN maintenance was hypothesized by Visani et al,6 we remark that 1 of our 2 cases already had prolonged HCR prior to receiving IFN and remains in HCR 2 years after IFN discontinuation. Unfortunately, only a few Q-PCR determinations were made in our cases, and so we are unable to establish whether IFN really exerted a control on the leukemic clone. Further studies are needed in order to verify the real frequency of PCR-detectable MRD in long-term remission of BCR/ABL-positive ALL. The use of prospective Q-PCR evaluation in more patients with persistently detectable BCR/ABL transcripts should provide important information on the effect of IFN or newly developed agents (ie, tyrosine kinase inhibitors) in the control of the disease.