Early detection of minimal residual disease by reverse transcriptase polymerase chain reaction predicts relapse in acute promyelocytic leukemia

Abstract

The PML/RAR alpha fusion RNA can be detected in acute promyelocytic leukemia (APL), cytogenetically characterized by the translocation t(15;17). Our study included ten newly diagnosed patients with APL who were investigated during the course of their diseases using reverse transcription polymerase chain reaction (RT-PCR). At diagnosis, aberrant fragments with a size heterogeneity due to alternative spliced products were detected in all patients, we observed breakpoints within bcr3 (short type) in two patients and bcr1 and 2 breakpoints (long type) in eight patients. Treatment consisted of all-trans retinoic acid (ATRA) in all patients; six patients received simultaneous cytostatic therapy during remission induction. At the time of complete hematological remission (CR), only two patients showed a negative RT-PCR result; eight of the ten patients were still PCR positive when nested primers were used. Subsequently, eight patients received consolidation chemotherapy and became PCR negative. Seven of eight patients are in continuous complete remission (median remission duration: 21 months, range: 11+ -26+ months). One patient of the chemotherapy group became PCR positive after 4 months in complete remission and relapsed after 6 months. The remaining two patients who were treated only with ATRA relapsed, received induction chemotherapy, and are in second and third complete remission, respectively. In conclusion. PCR negativity can be achieved only by chemotherapeutic consolidation; patients treated with ATRA alone remain PCR positive. Relapse is always preceded by a positive PCR result. Surprisingly, also patients without measurable PML/RAR alpha-mRNA in sequential analyses after cytostatic treatment became PCR positive and experienced relapse.

Monitoring of acute myeloid leukemia by flow cytometry

“…Early reports applying nonquantitative PCR indicate that long-term remissions in patients with acute promyelocytic leukemia are associated with PCR negativity [46][47][48][49][50][51][52][53][54], whereas persistently positive or recurring PCR results identify patients at very high risk of relapse [46,[49][50][51][53][54][55][56][57]. In many of these patients, salvage therapy is initiated before overt relapse of the disease [58].…”

Detection of residual aneuploid leukemic cells by “Continuous Gating”

“…Therefore, the combination of only one FITC-conjugated surface marker found on the tumor-cells combined with propidium iodide staining is a common method. Aberrant density of surface markers on leukemic cells can be found for several markers like CD45 or CD34 (5). Beside aberrant combinations of surface markers, density measurements of antigens on leukemic cells can be helpful in the detection of minimal residual disease (3,6,7).…”