O valor prognóstico da quantificação da carga leucêmica ao diagnóstico utilizando o gene GUS como gene controle em pacientes com Leucemia Mieloide Crônica

Abstract

Chronic myeloid leukemia (CML) is a hematologic malignancy characterized by the presence of a reciprocal translocation between chromosomes 9 and 22, resulting in a marker chromosome called "Philadelphia" (Ph). The fusion gene formed (BCR –ABL) leads to the production of a messenger RNA and expression of chimeric fusion protein (BCR -ABL) with constitutive tyrosine kinase activity, deregulating several signaling pathways and causing, for example, increased cell proliferation, resistance to apoptosis, and modification of the characteristics of cell adhesion. The development of the first target-specific inhibitory drug of tyrosine kinase (ITK) activity and its introduction into clinical practice radically changed the treatment of CML and made it necessary to establish new parameters for defining therapeutic response. Such a response is established according to increasing levels of sensitivity: Hematologic response (HR), Cytogenetic Response (CgR) or Molecular Response (MR). Aiming a standardization of clinical management, the European Consortium LeukemiaNet (ELN) grouped patients with CML in different operational response categories. The required time to a patient reach MR is considered an early predictor of therapeutic response throughout his clinical course. Recent studies establishing an association between early MR obtaining and durability of complete CgR. In 2013, such response categories were updated taking into account the existence of 2nd generation ITK and molecular assessment already at three months after initiation of ITK. Thus, the concept of the value of MR at three months is now the hallmark of early response, with greater prognostic value independent of other parameters. Therefore, the application of an appropriate internal control methodology is essential for an accurate determination of RM. To correct the variations in RNA quality and quantity and to calculate the sensitivity of the measurement by real-time PCR (qRT -PCR), a control gene (CG) of the transcript should be amplified in parallel to the fusion gene. Studies have shown that the CG BCR and ABL, the most widely used, do not have linearity when transcript levels are elevated (> 10%), because they have interference with the BCR-ABL gene fusion with false values. Thus, the question if the leukemic burden at diagnosis and the rate of decay of this burden can be used as predictive early biomarkers and therapeutic response, this question can not be answered with the use of ABL and BCR GC. In this study, 204 patients were analyzed for correlation between CgR and transcripts levels BCR-ABL/ABLEI average of 0.6% (n = 97) where BCR-ABL/ABLEI < 1 % (p < 0, 0001). It was possible to evaluate 31 patients for the study GUS gene as the molecular GC reviews . By measuring the levels of BCR-ABL at diagnosis, patients classified as responders had levels BCR-ABL/ABL% of 87.84 (26.8 to 164.5) and levels of BCR-ABL/GUS% of 28.38 (8.2 to 217) (p < 0.0001). Patients classified as non-responders had levels BCR-ABL/ABL% of 93.72 (30.87 to 184.5) and levels of BCR-ABL/GUS% of 40.92 (17.21 to 96.85) (p = 0.89)