Relapse and cytogenetic evolution in myeloid neoplasms

Based on the current WHO Classification of Myeloid Neoplasms, cytogenetic findings play a central role in the diagnostic classification of the myeloid malignancies. Cytogenetic abnormalities detected at primary diagnosis may change over time. Karyotype changes can be characterized as cytogenetic evolution, cytogenetic regression or a combination of both. While the exact mechanism of cytogenetic evolution is not completely understood, the process of cytogenetic evolution is not random, but follows different, and often disease-specific patterns during progression and relapse of myeloid neoplasms. Important lessons were learned from the cytogenetic evolution pathways observed over the course of chronic myelogenous leukemia (CML), progressing through chronic phase into accelerated phase and blast crisis. Cytogenetic evolution pathways of CML are divided into major and minor route abnormalities. The major route changes include an extra Ph chromosome (+Ph) trisomy 8 (+8) and the occurrence of an i(17q). The six most common minor route abnormalities include -7, -17, +17, +21 and -Y and one structural change, t(3;21). Recently an increased number of CML cases with karyotype abnormalities in Ph-negative cells have been reported in patients treated with imatinib. These abnormalities include trisomy 8, abnormalities of chromosome 7, and chromosome 20. The significance of the Ph-negative karyotype changes in subsequent development of myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) is unclear. Nevertheless, the occurrence of clonal abnormalities in Ph-negative cells underlines the importance of conventional cytogenetic studies in monitoring of CML patients. In AML, karyotype changes commonly occur between diagnosis and relapse status post chemotherapy. Karyotype evolution seems more common in patients who had unfavorable aberrations at diagnosis as compared to patients with favorable or intermediate abnormalities. Karyotype evolution results in shortened remission duration as compared to cases without cytogenetic change. Recent studies on cytogenetic evolution at relapse after allogeneic hematopoietic cell transplantation (allo-HCT) were similar to the data observed in chemotherapy-treated AML. Serial bone marrow evaluations after allo-HCT offer insights into the dynamics of karyotype evolution, notably, they demonstrated that a detection of karyotype abnormalities is usually followed by a relapse within the next 90 days. As a contrast, karyotype abnormalities were not observed in patients who do not relapse in the next 3 months. CGE at relapse was associated with significantly decreased postrelapse and post-transplantation survival compared with the non-CGE group. Very few data exist regarding a potential association between the dose or certain types of chemotherapy and cytogenetic evolution. Based on the results of a single study conducted recently, no specific chemotherapy regimen emerged to predispose for cytogenetic evolution. Further studies are necessary to evaluate the impact of the altered bone marrow environment and immunosuppression on karyotype stability.