The interleukin 3 gene is located on human chromosome 5 and is deleted in myeloid leukemias with a deletion of 5q.

The gene IL-3 encodes interleukin 3, a hematopoietic colony-stimulating factor (CSF) that is capable of supporting the proliferation of a broad range of hematopoietic cell types. By using somatic cell hybrids and in situ chromosomal hybridization, we localized this gene to human chromosome 5 at bands q23-31, a chromosomal region that is frequently deleted [del(5q)] in patients with myeloid disorders. By in situ hybridization, IL-3 was found to be deleted in the 5q-chromosome of one patient with refractory anemia who had a del(5)(q15q33.3), of three patients with refractory anemia (two patients) or acute nonlymphocytic leukemia (ANLL) de novo who had a similar distal breakpoint [del(5)(q13q33.3)], and of a fifth patient, with therapy-related ANLL, who had a similar distal breakpoint in band q33 [del(5)(q14q33.3)]. Southern blot analysis of somatic cell hybrids retaining the normal or the deleted chromosome 5 from two patients with the refractory anemia 5q- syndrome indicated that IL-3 sequences were absent form the hybrids retaining the deleted chromosome 5 but not from hybrids that had a cytologically normal chromosome 5. Thus, a small segment of chromosome 5 contains IL-3, GM-CSF (the gene encoding granulocyte-macrophage-CSF), CSF-1 (the gene encoding macrophage-CSF), and FMS (the human c-fms protooncogene, which encodes the CSF-1 receptor). Our findings and earlier results indicating that GM-CSF, CSF-1, and FMS were deleted in the 5q-chromosome, suggest that loss of IL-3 or of other CSF genes may play an important role in the pathogenesis of hematologic disorders associated with a del(5q).     

Assignment of CSF-1 to 5q33.1: evidence for clustering of genes regulating hematopoiesis and for their involvement in the deletion of the long arm of chromosome 5 in myeloid disorders.

The CSF-1 gene encodes a hematopoietic colony-stimulating factor (CSF) that promotes growth, differentiation, and survival of mononuclear phagocytes. By using somatic cell hybrids and in situ hybridization, we localized this gene to human chromosome 5 at bands q31 to q35, a chromosomal region that is frequently deleted [del(5q)] in patients with myeloid disorders. By in situ hybridization, the CSF-1 gene was found to be deleted in the 5q- chromosome of a patient with refractory anemia who had a del(5)(q15q33.3) and in that of a second patient with acute nonlymphocytic leukemia de novo who had a similar distal breakpoint [del(5)(q13q33.3)]. The gene was present in the deleted chromosome of a third patient, with therapy-related acute nonlymphocytic leukemia, who had a more proximal breakpoint in band q33 [del(5)(q22q33.1)]. Hybridization of the CSF-1 probe to metaphase cells of a fourth patient, with acute nonlymphocytic leukemia de novo, who had a rearrangement of chromosomes 5 and 21 [ins(21;5)(q22;q31.3q33.1)] resulted in labeling of the breakpoint junctions of both rearranged chromosomes; this suggested that CSF-1 is located at 5q33.1. Thus, a small segment of chromosome 5 contains GM-CSF (the gene encoding the granulocyte-macrophage CSF), CSF-1, and FMS, which encodes the CSF-1 receptor, in that order from the centromere; this cluster of genes may be involved in the altered hematopoiesis associated with a deletion of 5q.     

Molecular organization of the cytokine gene cluster, involving the human IL-3, IL-4, IL-5, and GM-CSF genes, on human chromosome 5

The human genes for the hematopoietic growth factors interleukin-3 (IL-3), IL-5, and granulocyte-macrophage colony-stimulating factor (GM-CSF) have been mapped to 5q23-31. We present in situ hybridization evidence that the human IL-4 gene is located at 5q23.3-31.2, suggesting that the four cytokine genes may be closely linked. We used pulsed-field gel electrophoresis to prepare subchromosomal restriction maps surrounding these genes to define this possible linkage more precisely. The IL-4 and IL-5 genes are tightly linked, being 90 to 240 kilobases (kb) apart, as has been shown for the IL-3 and GM-CSF genes, which are only 9 kb apart. Possible overlap of the map containing the IL-4 and IL-5 genes with restriction sites 5' to the IL-3 gene suggests that the four cytokine genes may be localized within 500 kb of each other. The endothelial cell growth factor gene (ECGF), which has also been localized to the 5q31 region, did not appear to be close to the cytokine genes. Linkage of the IL-3, IL-4, IL-5, and GM-CSF genes has important implications in the evolutionary origin and regulation of expression of these genes. The four cytokine genes are located in the region of the long arm of chromosome 5, which is deleted in the 5q- anomaly. The present study provides a basis for further investigations of this disorder.     

Lenalidomide inhibits the malignant clone and up-regulates the SPARC gene mapping to the commonly deleted region in 5q- syndrome patients

Myelodysplastic syndromes (MDSs) are a group of hematopoietic stem cell disorders characterized by ineffective hematopoiesis and peripheral blood cytopenias. Lenalidomide has dramatic therapeutic effects in patients with low-risk MDS and a chromosome 5q31 deletion, resulting in complete cytogenetic remission in >60% of patients. The molecular basis of this remarkable drug response is unknown. To gain insight into the molecular targets of lenalidomide we investigated its in vitro effects on growth, maturation, and global gene expression in isolated erythroblast cultures from MDS patients with del(5)(q31). Lenalidomide inhibited growth of differentiating del(5q) erythroblasts but did not affect cytogenetically normal cells. Moreover, lenalidomide significantly influenced the pattern of gene expression in del(5q) intermediate erythroblasts, with the VSIG4, PPIC, TPBG, activin A, and SPARC genes up-regulated by >2-fold in all samples and many genes involved in erythropoiesis, including HBA2, GYPA, and KLF1, down-regulated in most samples. Activin A, one of the most significant differentially expressed genes between lenalidomide-treated cells from MDS patients and healthy controls, has pleiotropic functions, including apoptosis of hematopoietic cells. Up-regulation and increased protein expression of the tumor suppressor gene SPARC is of particular interest because it is antiproliferative, antiadhesive, and antiangiogenic and is located at 5q31-q32, within the commonly deleted region in MDS 5q- syndrome. We conclude that lenalidomide inhibits growth of del(5q) erythroid progenitors and that the up-regulation of SPARC and activin A may underlie the potent effects of lenalidomide in MDS with del(5)(q31). SPARC may play a role in the pathogenesis of the 5q- syndrome.     

Interleukin-5 is at 5q31 and is deleted in the 5q- syndrome

Human interleukin-5 (IL-5) is a selective eosinophilopoietic and eosinophil-activating growth hormone. By in situ hybridization this gene is mapped to chromosome 5q23.3 to 5q32. It is shown to be deleted in two patients with the 5q-syndrome and in one patient previously diagnosed with myelodysplasia whose condition had progressed to acute myeloblastic leukemia. The clustering of other genes involved in hematopoiesis (IL-3, granulocyte-macrophage colony-stimulating factor, feline sarcoma viral oncogene homolog, colony-stimulating factor 1) to the same region as IL-5 suggests a nonrandom localization and raises interesting questions concerning the evolution and regulation of these genes.     

Loss of both CSF1R (FMS) alleles in patients with myelodysplasia and a chromosome 5 deletion.

A high proportion of patients with myelodysplasia show characteristic karyotypic abnormalities in bone marrow cells. The most distinctive of the myelodysplastic syndromes is the 5q- syndrome characterized by refractory anemia, poorly lobulated megakaryocytes, and an interstitial deletion of the long arm of chromosome 5 (5q deletion) as the sole karyotypic abnormality. Recently, several genes encoding hemopoietic growth factors and receptors, comprising the interleukins 3, 4, and 5, macrophage colony-stimulating factor, granulocyte/macrophage-colony-stimulating factor, and the receptor for macrophage-colony-stimulating factor [the CSF1R (formerly FMS) gene product], have been localized to the long arm of chromosome 5, and there has been much speculation that deletion of one or more of these genes may be critical to the pathogenesis of the associated myeloid disorders. One candidate gene is CSF1R, which is required for normal proliferation and differentiation of hemopoietic cells of the myeloid lineage. We have carried out a molecular examination of the CSF1R, both on the 5q- chromosome and on the apparently normal homologous chromosome 5, in 10 patients with myelodysplasia and a 5q deletion. We have found, using restriction fragment length polymorphism analysis and gene dosage experiments, that all 10 patients showed deletion of CSF1R; 6 of 10 were hemizygous and 4 of 10 homozygous for CSF1R loss. The homozygous CSF1R loss has been confirmed in 2 patients by an in situ hybridization technique comparing the signal in affected cells to that in control sex-mismatched cells on the same slides. In those patients considered to have homozygous CSF1R loss by DNA experiments the gene was deleted from the 5q chromosome in all cells and from the apparently normal chromosome 5 in a subset of cells. This loss of one CSF1R allele, together with loss in some cells of the remaining allele on the homologous chromosome 5, in patients with myelodysplasia indicates that this is a region of critical gene loss on 5q. The loss of the hemopoietic growth factor receptor gene CSF1R may be important in the pathogenesis of human myeloid leukemia.     

Van-den Berghe's 5q- syndrome in 2008

Van Den Berghe established 5q- syndrome as a discrete clinical entity in 1974 when he described patients with macrocytic anaemia, thrombocytosis, dyserythropoiesis, hypolobulated megakaryocytes and an interstitial deletion within chromosome 5q. With del(5q) as the sole cytogenetic abnormality, 5q- syndrome represents an opportunity to define precisely the molecular defect(s) underlying the pathogenesis of this disease. The commonly deleted region in 5q- syndrome, which is distinct from that in patients with complex cytogenetic changes that include del(5q), includes the ribosomal protein S14 locus and it has been proposed that that loss of an RPS14 allele accounts for the 5q- syndrome phenotype. However, this hypothesis fails to explain the growth advantage of the 5q- syndrome clone and it is evident that ribosomal protein defects are not specific to 5q- syndrome, as they are found in other bone marrow failure syndromes. Lenalidomide therapy leads to normalization of both haematological and cytogenetic parameters in the majority of 5q- syndrome patients. This review examines the potential role of several genes, including RPS14 , in the pathogenesis of the 5q- syndrome and recent advances in clinical management, with particular emphasis on the role and mechanism of action of lenalidomide.     

The human interleukin-1 alpha gene is located on the long arm of chromosome 2 at band q13

Interleukin-1 alpha (IL-1 alpha) and interleukin-1 beta (IL-1 beta) are two biochemically distinct, but distantly related, polypeptidic cytokines that play a key role in inflammation, immunologic reactions, and tissue repair. Recently, it has been shown that IL-1 alpha is identical to hematopoietin 1, which was described as a hematopoietic growth factor acting on early progenitor cells in synergy with other hematopoietic growth factors. In this report we discuss our use of in situ hybridization on human prometaphase cells with a human IL-1 alpha cDNA probe to localize the human IL-1 alpha gene on the proximal part of the long arm of chromosome 2 at band q13, in the same chromosomal region as the IL-1 beta gene.     

The 5q- syndrome

The 5q- syndrome is a distinct hematological disorder with typical laboratory, morphological, cytogenetic, molecular, and prognostic features. It is defined as a myelodysplastic syndrome with a medullary blast count <5% and an isolated interstitial deletion of the long arm of chromosome 5, including bands q31-q33. The molecular basis of this disease has not yet been fully elucidated, but there is evidence that a commonly deleted region of 1.5 Mb harbors one or several tumor suppressor genes, the loss of which being the basic event leading to disease activity. The 5q- deletion has been demonstrated in very early hematopoietic precursors, including CD34+CD133+ and CD34+CD38-Thyl+ cells. Analysing data of 60 patients with the 5q- syndrome that were followed over a period of up to 28 years, we found a median age at diagnosis of 66.8 years and a female preponderance with a male to female ratio of 1:1.5. Anemia is usually macrocytic and combined with low reticulocyte counts and high erythropoetin levels. Three types of cytogenetic deletion are most prevalent: del(5)(q13q33), del(5)(q13q31) and del(5)(q22q33). The 5q- syndrome has a good prognosis with a median overall survival of 107 months at a median follow-up of 53 months, and a low probability of transformation to AML. An increase of the medullary blast count to > or =5% or the addition of one karyotypic anomaly severely reduces median overall survival. The most promising therapeutic approach is the novel thalidomide analogue CC5013 that is currently evaluated in an international phase II study.     

Translocations and deletions of 5q13.1 in myelodysplasia and acute myelogenous leukemia: evidence for a novel critical locus

Acquired partial and complete deletions of chromosome 5 (5q-, -5) are common cytogenetic anomalies associated with myelodysplasia (MDS) and acute myeloid leukemia (AML). A critical region of consistent loss at 5q31.1 (in > 90% of cases) has led us and others to postulate the presence of a key negative regulator(s) of leukemogenesis. Although the interstitial deletion limits vary among patients, del(5) (q13q33) and del(5)(q13q35) constitute major subsets. Furthermore, it is not rare to encounter deletions, translocations, or paracentric inversions involving 5q11 to 5q13, which indicates inactivation or disruption of important gene(s) at that locus. In this report, we have localized a novel locus at 5q13.1 to a 2.0-Mb interval between the anonymous markers D5S672 and GATA-P1804. This locus resided within the region of loss in 12 of 27 patients with anomalies of chromosome 5; one of these cases had apparent retention of both alleles of all the telomeric loci. Fluorescence in situ hybridization (FISH) studies demonstrate that the AML cell line ML3 is disrupted at 5q13.1 by a translocation involving chromosome 3, with apparent retention of the entire chromosome 5 sequence. Our results suggest that this novel proximal locus encodes a critical gene that may be deleted or disrupted in a subset of MDS/AML patients with chromosome 5 anomalies.     

Isolation and characterization of hematopoietic progenitor/stem cells in 5q-deleted myelodysplastic syndromes: evidence for involvement at the hematopoietic stem cell level

Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal disorders characterized by ineffective hematopoiesis and frequent progression to acute myeloid leukemia. Within MDS, 5q- syndrome constitutes a distinct clinical entity characterized by an isolated deletion of the long arm of chromosome 5 (5q-), a relatively good prognosis, and infrequent transformation to acute leukemia. The cell of origin in 5q- syndrome as well as in other 5q-deleted MDS patients has not been established, but evidence for involvement of multiple myeloid (but not lymphoid) lineages has suggested that a myeloid-restricted progenitor rather than a pluripotent (lympho-myeloid) stem cell might be the primary target in most patients. Although in 9 patients no evidence of peripheral blood T-cell and only 1 case of B-cell involvement was found, the data herein support that 5q deletions occur in hematopoietic stem cells (HSCs) with a combined lympho-myeloid potential. First, in all investigated patients a minimum of 94% of cells in the minor CD34(+)CD38(-) HSC compartment were 5q deleted as determined by fluorescence in situ hybridization. Second, in 3 of 5 patients 5q aberrations were detected in a large fraction (25% to 90%) of purified CD34(+)CD19(+) pro-B cells. Furthermore, extensive functional characterization with regard to responsiveness to early-acting cytokines, long-term culture-initiating cells, and nonobese diabetic/severe combined immunodeficiency repopulating cells supported that MDS HSCs in 5q-deleted patients are CD34(+)CD38(-), but inefficient at reconstituting hematopoiesis.     

c-src is consistently conserved in the chromosomal deletion (20q) observed in myeloid disorders.

The proto-oncogene c-src has been mapped to two bands in human chromosomes, 1p36 and 20q13, both of which are involved in rearrangements in human tumors. In particular, deletions (loss of part of a chromosome) of the long arm of chromosome 20, del(20q), are commonly observed in hematologic malignant diseases. By using in situ chromosomal hybridization of a c-src probe to metaphase cells prepared from leukemic bone marrow cells of three patients with a del(20q), we observed specific labeling on the deleted chromosome in each patient, indicating that the c-src locus was conserved. The presence on the rearranged chromosomes of c-src, which is normally located on the most distal band of 20q, indicated that the deletions were not terminal as they appeared to be on the basis of chromosome morphology, but rather that they were interstitial. The location of c-src relative to the distal breakpoint in these deletions is unknown. By using the v-src probe in Southern blot analysis of genomic DNA from three patients with a del(20q), we found that no major genomic rearrangements or amplification of the c-src genes had occurred within the regions homologous to v-src. Our observation that c-src is consistently preserved in these rearranged chromosomes suggests that this gene may play a role in the pathogenesis of some myeloid disorders.     

Allelic loss of IRF1 in myelodysplasia and acute myeloid leukemia: retention of IRF1 on the 5q- chromosome in some patients with the 5q- syndrome

Acquired interstitial deletions of the long arm of chromosome 5 occur frequently in the myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Recently IRF1, a putative tumor suppressor gene localized to the long arm of chromosome 5, has been shown to be deleted from the 5q- chromosome in a group of patients with MDS and AML. It has been suggested that the loss of IRF1 may be critical to the development of the 5q- syndrome. We have investigated the allelic loss of IRF1 in a group of 12 patients with MDS and a 5q deletion and 2 patients with AML and a 5q deletion. Gene dosage experiments demonstrated that 12 of 14 patients had loss of one allele of the IRF1 gene but no evidence of homozygous loss and that 2 patients with 5q- syndrome retained both copies of the gene. The retention of IRF1 on the 5q- chromosome in these two cases has been confirmed by fluorescent in situ hybridization localization using an IRF1 cosmid. Pulsed field gel electrophoresis was used to determine whether there was any evidence for structural rearrangement in the region encompassing the IRF1 gene in these two patients. No aberrant bands were detected with a range of rare cutter enzyme digests. We conclude that IRF1 maps outside the commonly deleted segment of the 5q- chromosome and that loss of IRF1 is not solely responsible for the development of the 5q- syndrome.     

A new recurrent translocation, t(5;11)(q35;p15.5), associated with del(5q) in childhood acute myeloid leukemia. The UK Cancer Cytogenetics Group (UKCCG)

Partial deletion of the long arm of chromosome 5, del(5q), is the cytogenetic hallmark of the 5q-syndrome, a distinct subtype of myelodysplastic syndrome-refractory anemia (MDS-RA). Deletions of 5q also occur in the full spectrum of other de novo and therapy-related MDS and acute myeloid leukemia (AML) types, most often in association with other chromosome abnormalities. However, the loss of genetic material from 5q is believed to be of primary importance in the pathogenesis of all del(5q) disorders. In the present study, we performed fluorescence in situ hybridization (FISH) studies using a chromosome 5-specific whole chromosome painting probe and a 5q subtelomeric probe to determine the incidence of cryptic translocations. We studied archival fixed chromosome suspensions from 36 patients with myeloid disorders (predominantly MDS and AML) and del(5q) as the sole abnormality. In 3 AML patients studied, this identified a translocation of 5q subtelomeric sequences from the del(5q) to the short arm of an apparently normal chromosome 11. FISH with chromosome 11-specific subtelomeric probes confirmed the presence of 11p on the shortened 5q. Further FISH mapping confirmed that the 5q and 11p translocation breakpoints were the same in all 3 cases, between the nucleophosmin (NPM1) and fms-related tyrosine kinase 4 (FLT4) genes on 5q35 and the Harvey ras-1-related gene complex (HRC) and the radixin pseudogene (RDPX1) on 11p15.5. Importantly, all 3 patients with the cryptic t(5;11) were children: a total of 3 of 4 AML children studied. Two were classified as AML-M2 and the third was classified as M4. All 3 responded poorly to treatment and had short survival times, ranging from 10 to 18 months. Although del(5q) is rare in childhood AML, this study indicates that, within this subgroup, the incidence of cryptic t(5;11) may be high. It is significant that none of the 24 MDS patients studied, including 11 confirmed as having 5q-syndrome, had the translocation. Therefore, this appears to be a new nonrandom chromosomal translocation, specifically associated with childhood AML with a differentiated blast cell phenotype and the presence of a del(5q).     

Molecular genetics of myeloid leukemia: identification of the commonly deleted segment of chromosome 20

A deletion of the long arm of chromosome 20 [del(20q)] is a recurring abnormality in malignant myeloid disorders. The occurrence of the del(20q) in a broad spectrum of myeloid disorders suggests that the loss of genetic material on 20q could provide a proliferative advantage to myeloid cells, possibly through the loss of a tumor-suppressor gene. We have examined a series of patients with the del(20q) using fluorescence in situ hybridization (FISH) with unique sequence probes that map along the length of 20q, and have delineated a segment that is deleted in 95% of all patients examined (18 of 19). In addition, we have shown that the deletions are interstitial rather than terminal. This region of deletion extends from 20q11.2 to q12, and is flanked by the RPN2 (proximal) and D20S17 loci (distal). The SRC and ADA genes are located within the commonly deleted segment. Our findings emphasize the importance of FISH and other molecular mapping techniques in defining such a region. The delineation of a commonly deleted segment in 20q11.2- q12 will facilitate the identification of candidate tumor-suppressor genes on 20q.     

T-cell receptor alpha-chain gene is split in a human T-cell leukemia cell line with a t(11;14)(p15;q11).

Chromosomal rearrangements in malignant T-cell disease frequently involve the chromosome bands containing the T-cell receptor genes. The RPMI 8402 cell line, which was established from the leukemia cells of a patient with T-cell acute lymphoblastic leukemia, is characterized by a translocation involving chromosome 14 (band q11) and chromosome 11 (band p15) [t(11;14)(p15;q11)]. By using in situ chromosomal hybridization and Southern blot analysis to examine RPMI 8402 cells, we determined that the break at 14q11 occurs within the variable region sequences of the T-cell receptor alpha-chain gene (TCRA); the break at 11p15 occurs between the HRAS1 gene and the genes for insulin and the insulin-like growth factor 2. These results suggest that the TCRA sequences activate a cellular gene located at 11p15 in malignant T-cell disorders.     

Hematological Malignancies

The 5q- syndrome is a distinct hematological disorder with typical laboratory, morphological, cytogenetic, molecular, and prognostic features. It is defined as a myelodysplastic syndrome with a medullary blast count <5% and an isolated interstitial deletion of the long arm of chromosome 5, including bands q31-q33. The molecular basis of this disease has not yet been fully elucidated, but there is evidence that a commonly deleted region of 1.5 Mb harbors one or several tumor suppressor genes, the loss of which being the basic event leading to disease activity. The 5q- deletion has been demonstrated in very early hematopoietic precursors, including CD34+CD133+ and CD34+CD38?Thyl+ cells. Analysing data of 60 patients with the 5q- syndrome that were followed over a period of up to 28 years, we found a median age at diagnosis of 66.8 years and a female preponderance with a male to female ratio of 1:1.5. Anemia is usually macrocytic and combined with low reticulocyte counts and high erythropoetin levels. Three types of cytogenetic deletion are most prevalent: del(5)(q13q33), del(5)(q13q31) and del(5)(q22q33). The 5q- syndrome has a good prognosis with a median overall survival of 107 months at a median follow-up of 53 months, and a low probability of transformation to AML. An increase of the medullary blast count to ≥5% or the addition of one karyotypic anomaly severely reduces median overall survival. The most promising therapeutic approach is the novel thalidomide analogue CC5013 that is currently evaluated in an international phase II study.     

Clinical characteristics and prognosis of 50 patients with a myeloproliferative syndrome and deletion of part of the long arm of chromosome 5

Of 50 consecutive patients (30 female and 20 male; median age, 70 years) with a myeloproliferative disorder and a 5q- chromosome, 12 (24%) had refractory anemia, 16 (32%) had refractory anemia with excess blasts, 13 (26%) had acute nonlymphocytic leukemia, six (12%) had the 5q- syndrome, and three (6%) had an unclassifiable myeloproliferative disease. Twenty-five patients had only a 5q- anomaly (group 1), and 25 had a 5q- plus additional chromosome abnormalities (group 2). Four types of 5q- anomalies were recognized: a del(5)(q13q33) occurred in 39 patients, a del(5)(q31q35) in nine, a del(5)(q22q33) in one, and a del(5)(q13q35) in one. The survival distribution for patients in group 1 was significantly better (P = .012) than for those in group 2. Cox-model analyses indicated that having a 5q- chromosome and other abnormalities is significantly (P less than .01) associated with poor survival even after adjustment for the effects of other important factors such as type of disease, age, and sex. The two groups had similar distributions of most variables, including age, sex, and disease types. However, patients in group 1 had a significantly higher platelet count and mean corpuscular volume than those in group 2. Only two patients in group 1 had had prior chemotherapy, but nine in group 2 had had either prior chemotherapy or radiation or both, and one patient in group 2 had had heavy exposure to pesticides.     

Design and validation of DNA probe sets for a comprehensive interphase cytogenetic analysis of acute myeloid leukemia

The objective of this study was to design DNA probe sets that enable the detection of chromosome aberrations in acute myeloid leukemia (AML) by interphase cytogenetics using fluorescence in situ hybridization (FISH) and to compare the results of interphase cytogenetics with those of conventional chromosome banding analysis. One hundred five consecutive patients with adult AML entered on a multicenter treatment trial were studied with a comprehensive set of DNA probes recognizing the most relevant AML-associated structural and numerical chromosome aberrations: translocations t(8;21), t(15;17), and t(11q23); inversion inv(16);chromosomal deletions (5q-, 7q-, 9q-, 12p-, 13q-, 17p-, and 20q- ); and chromosomal aneuploidies. Interphase cytogenetics was particularly sensitive for detecting the AML-specific gene fusions: 3 additional cases of inv(16) and 1 additional case of t(8;21) were identified by FISH that were missed by banding analysis, whereas equal numbers of t(11q23) and t(15;17) were detected. Five additional cases of trisomy 8q, 3 more cases of trisomy 11q, and 2 more cases of trisomies 21q and 22q were shown by FISH. These aberrations were either masked in complex karyo-types or identified in cases in which conventional banding analysis failed. On the other hand, the DNA probes selected were not informative to detect 1 case of 5q-, 9q-, and 20q-. In 5 cases, clonal aberrations were detected on banding analysis for which no FISH probes were selected. In conclusion, interphase cytogenetics proved to be more sensitive for detecting AML-specific chimeric gene fusions and some partial trisomies. Interphase cytogenetics provides a powerful technique complementary and, with further development of diagnostic DNA probes, even an alternative to chromosome banding studies for the cytogenetic analysis of AML.