Double minutes (dmin)-circular, extra-chromosomal amplifications of specific acentric DNA fragments-are relatively frequent in malignant disorders, particularly in solid tumors. In acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS), dmin are observed in approximately 1% of the cases. Most of them consist of an amplified segment from chromosome band 8q24, always including the MYC gene. Besides this information, little is known about their internal structure. We have characterized in detail the genomic organization of 32 AML and two MDS cases with MYC-containing dmin. The minimally amplified region was shown to be 4.26 Mb in size, harboring five known genes, with the proximal and the distal amplicon breakpoints clustering in two regions of approximately 500 and 600 kb, respectively. Interestingly, in 23 (68%) of the studied cases, the amplified region was deleted in one of the chromosome 8 homologs at 8q24, suggesting excision of a DNA segment from the original chromosomal location according to the 'episome model'. In one case, sequencing of both the dmin and del(8q) junctions was achieved and provided definitive evidence in favor of the episome model for the formation of dmin. Expression status of the TRIB1 and MYC genes, encompassed by the minimally amplified region, was assessed by northern blot analysis. The TRIB1 gene was found over-expressed in only a subset of the AML/MDS cases, whereas MYC, contrary to expectations, was always silent. The present study, therefore, strongly suggests that MYC is not the target gene of the 8q24 amplifications.

No abstract

Cerebral involvement is an uncommon complication of multiple myeloma. We report on a 64-year-old man hospitalized for a partial seizure. MRI showed two intracerebral lesions, which proved to be plasmacytomas. After complete staging, we retained the diagnosis of immunoglobulin G lambda-type multiple myeloma with CNS involvement. Cytogenetic analysis of plasma cells detected a deletion in the p53 gene at 17p13.1. Despite cranial radiotherapy and systemic chemotherapy, the patient's disease progressed rapidly and he died five months after diagnosis. What makes this case unusual is that overt multiple myeloma had been absent before cerebral involvement was discovered. It confirms the extremely poor prognosis of patients with CNS myeloma even in the presence of aggressive treatment. Cytogenetic abnormalities could be a marker of chromosomal and genetic instability, conferring to multiple myeloma a more aggressive profile.

No abstract

Systemic mastocytoses represent neoplastic proliferations of mast cells. In about 20% of cases systemic mastocytoses are accompanied by clonal haematopoietic non-mast cell-lineage disorders, most commonly myeloid neoplasms. A case of systemic mastocytosis carrying the characteristic mutation at codon 816 (D816V) in the KIT gene of mast cells, with two concurrent accompanying clonal haematopoietic non-mast cell-lineage disorders, chronic myeloproliferative disease, unclassifiable and precursor B lymphoblastic leukaemia is documented. Both accompanying clonal haematopoietic non-mast cell-lineage disorders carried the wild-type KIT gene, but had a novel t(13;13)(q12;q22) involving the FLT3 locus at 13q12. The chronic myeloproliferative disease, unclassifiable and the precursor B lymphoblastic leukaemia were cured by syngenous stem cell transplantation, but the systemic mastocytosis persisted for more than 10 years. The additional impact of molecular techniques on the correct diagnosis in haematological malignancies is highlighted, and evidence is provided that, apart from internal tandem duplications and mutations, FLT3 can be activated by translocations.

for the relatively favorable outcome in this group. However, Keywords: inv(16)(p13q22); t(16;16)(p13;q22); 16 p deletions; FISH; acute myeloid leukemia; prognosis in another study, no difference in prognosis was observed between deletion and non-deletion patients. 18 To assess further the incidence of the 16 p deletions and to improve the understanding of their prognostic significance, we Introduction studied 15 patients with AML and inv(16) or t(16;16) by fluorescence in situ hybridization (FISH) using the zit14 cosmid In 1983, Arthur and Bloomfield 1,2 reported five patients with as a probe. Clinical, cytogenetic and FISH data are reported acute myeloid leukemia (AML) of myelomonocytic type (M4), here. increased marrow eosinophils and a structurally abnormal chromosome 16. Soon after, a pericentric inversion of chromosome 16, inv(16)(p13q22), was described in 18 patients Patients, materials and methods who had M4 leukemia and morphologically abnormal eosinophils with irregular, basophilic-staining granules and distinct Patients cytochemical properties. 3,4 A related chromosome abnormality, t(16;16)(p13;q22), was reported in one patient with Fifteen patients with either inv(16) or t(16;16) were diagnosed similar characteristics. 5 Further studies have suggested that at the divisions of hematology of the University Hospitals of these two abnormalities were uniquely associated with M4 Zü rich (four patients), Basel (three), Bern (three), Lausanne and abnormal eosinophils and the correlation between the (two) and of the Canton Hospitals of Sankt-Gallen (two) and karyotype and morphology has led to a subcategory in the Aarau (one) between 1992 and 1995 (Table 1). Each patient FAB classification, namely M4Eo. 6 However, both rearrangewas assigned a unique patient number for this and previous ments have been reported in other types of myeloid dispublications. [19][20][21] Additionally, 10 patients with AML (nine) or orders. 7,8 In most studies, the presence of inv(16)/t(16;16) has acute lymphoblastic leukemia (ALL) (one) and normal karyobeen associated with a high cure rate with standard chemotypes or aberrations other than inv(16) or t(16;16) were investitherapy and a relatively favorable prognosis. [9][10][11][12][13] gated by FISH and served as controls. Informed consent was Inv(16) and t(16;16) have been shown to involve, on 16p13, obtained from each patient. a smooth muscle myosin heavy chain gene (MYH11) and, onThe diagnosis and classification of patients were based on morphologic and cytochemical examination of peripheral blood (PB) films, bone marrow (BM) aspirate and biopsy speci-

No abstract

Microsatellites are important highly polymorphic genetic markers dispersed in the human genome. Using a panel of 22 (CA)n repeat microsatellite markers mapped to recurrent breakpoint cluster regions specifically involved in leukemia, we investigated 114 adult leukemias (25 acute lymphocytic leukemia [ALL], 32 acute myeloid leukemia [AML], 36 chronic lymphocytic leukemia [CLL], and 21 chronic myeloid leukemia [CML] in chronic phase) for somatic mutations at these loci. In each patient, DNA from fresh leukemia samples was analyzed alongside normal constitutive DNA from buccal epithelium. We detected loss of heterozygosity (LOH) in 81 of 114 patients (ALL 16/25, AML 25/32, CLL 30/36, CML 10/21). Deletions were most often seen in ALL at 11q23 and 19p13; in AML at 8q22 and 11q23; in CLL at 13q14.3, 11q13, and 11q23; and in CML at 3q26. Only six deletions were reported in 74 karyotypes analyzed, whereas in these same cases, 91 LOH events were detected by microsatellites. Of 26 leukemias with a normal karyotype, 16 nevertheless showed at least one LOH by microsatellite analysis. Replication errors were found in 10 of 114 patients (8.8%). Thus, microsatellite instability is rare in leukemia in contrast to many solid tumors. Our findings suggest that in adult leukemia, LOH may be an important genetic event in addition to typical chromosomal translocations. LOH may point to the existence of tumor suppressor genes involved in leukemogenesis to a degree that has hitherto been underestimated.