Cytogenetic and genetic analysis provides pathologists and clinicians with a powerful tool for the diagnosis and classification of hematologic malignant diseases. The detection of an acquired, somatic mutation establishes the diagnosis of a neoplastic disorder and rules out hyperplasia, dysplasia, or morphologic changes from toxic injury or vitamin deficiency. Specific cytogenetic and genetic abnormalities have been identified that are very closely, and sometimes uniquely, associated with morphologically distinct subsets of leukemia or lymphoma, enabling clinicians to predict their clinical course and likelihood of responding to particular treatments. The detection of one of these recurring abnormalities is helpful in establishing the diagnosis and adds information of prognostic importance. In many cases, the prognostic information derived from cytogenetic and genetic analysis is independent of that provided by other clinical features. Patients with favorable genetic prognostic features benefit from standard therapies with a well-known spectra of toxicities, whereas those with less-favorable clinical and cytogenetic or genetic characteristics may be better treated with more intensive or investigational therapies. Pretreatment cytogenetic analysis also can be useful in choosing between post-remission therapies that differ widely in cost, acute and chronic morbidity, and effectiveness. The appearance of new abnormalities in the karyotype of a patient under observation often signals clonal evolution and more aggressive behavior. The disappearance of a chromosomal abnormality present at diagnosis is an important indicator of complete remission following treatment, and its reappearance may herald disease recurrence.
Acronyms and Abbreviations:
ALCL, anaplastic large cell lymphoma; ALL, acute lymphocytic or lymphoblastic leukemia; AML, acute myeloid leukemia; AMML, acute myelomonocytic leukemia; APL, acute promyelocytic leukemia; CDS, commonly deleted segment; CLL, chronic lymphocytic leukemia; CMA, chromosome microarray analysis; CML, chronic myeloid leukemia; del, deletion; DLBCL, diffuse large B-cell lymphoma; EBV, Epstein-Barr virus; FAB, French-American-British; FISH, fluorescence in situ hybridization; FLT3, FMS-like tyrosine kinase; HSC, hematopoietic stem cell; IGH, immunoglobulin heavy chain; inv, inversion; ITD, internal tandem duplication; JAK, Janus kinase; LOH, loss of heterozygosity; MALT, mucosa-associated lymphoid tissue; MAPK, mitogen-activated protein kinase; MDS, myelodysplastic syndrome; Ph, Philadelphia chromosome; PI3K, phosphatidylinositide 3′-kinase; qRT-PCR, quantitative reverse transcriptase polymerase chain reaction; RA, refractory anemia; RAEB, refractory anemia with excess blasts; RARα, retinoic acid receptor-α; RARS, refractory anemia with ring sideroblasts; RARS-t, refractory anemia with ringed sideroblasts and thrombocytosis; RCMD, refractory cytopenia with multilineage dysplasia; SNP, single nucleotide polymorphism; STAT, signal transducer and activator of transcription; t, translocation; t-, therapy-related, TKI, tyrosine kinase inhibitor; WHO, World Health Organization.
GENETIC CONSEQUENCES OF GENOMIC REARRANGEMENTS
Over the past two decades, the genes that are located at the breakpoints of a number of the recurring chromosomal translocations have been identified. Alterations in the expression of the genes or in the properties of the encoded proteins resulting from the rearrangement play an integral role in the process of malignant transformation.1,2 The altered genes fall into several functional classes, including tyrosine or serine protein kinases, cell surface receptors, growth factors ...