Deletion 20q in association with Philadelphia chromosome positive acute lymphoblastic leukemia. A report of two cases

Deletion 20q12 is associated with histological transformation of nodal marginal zone lymphoma to diffuse large B-cell lymphoma

The genetic and molecular abnormalities underlying histological transformation (HT) of nodal marginal zone lymphoma (NMZL) to diffuse large B-cell lymphoma (DLBCL) are not well known. While del(20q12) is commonly deleted in myelodysplastic syndrome it has not previously been associated with DLBCL. We recently described a case of DLBCL harboring del(20q12) in a patient with a history of MZL involving lymph nodes and skin. Here we report eight matched cases of transformed MZL(tMZL): six from nodal MZL (tNMZL) and two from splenic MZL (tSMZL). We found >20% del(20q12) in 4/6 tNMZL, but not in tSMZL, nor in unmatched DLBCL, MZL with increased large cells (MZL-ILC), or MZL cases. To examine whether transformation is associated with a specific gene signature, the matched cases were analyzed for multiplexed gene expression using the Nanostring PanCancer Pathways panel. The differential gene expression signature revealed enrichment of inflammatory markers, as previously observed in MZL. Also, tMZL and de novo DLBCL were enriched for extracellular matrix proteins such as collagen and fibronectin, vascular development protein PDGFRβ, DNA repair protein RAD51, and oncogenic secrete protein Wnt11. A subset of genes is expressed differentially in del(20q12) tMZL cases vs non-del(20q12) tMZL cases. These results suggest a specific pathway is involved in the histological transformation of NMZL, which could serve as an indicator of aggressive clinical course in this otherwise indolent neoplasm.

Prognostic significance of del(20q) in patients with hematological malignancies

Deletions of the long arm of chromosome 20 represent a common chromosomal abnormality associated with myeloid malignancies, in particular with myeloproliferative disorders (MPD), myelodysplastic syndromes (MDS), and acute myeloid leukemia (AML). Using G-banding cytogenetic techniques, we found clones with del(20q) in 36 patients with hematological malignancies examined in our laboratory during the years 2001-2003: in 23 patients as a sole cytogenetic aberration and in 13 patients together with other chromosomal changes. Fluorescence in situ hybridization (FISH) with a probe specific for the 20q12 region was used in all cases to confirm the presence of the clone with deletion. For patients with additional or complex chromosomal rearrangements, multicolor FISH (M-FISH) analysis was performed. Statistical evaluation of the prognostic impact of sex, age, diagnosis, and karyotype was performed. The survival time correlated with the type of chromosomal aberration; no significant differences in survival were found for sex, age, and diagnosis.

Molecular differences between small and large cells in patients with chronic lymphocytic leukemia

The genetic events involved in the transformation of chronic lymphocytic leukemia (CLL) to Richter's syndrome (RS) are poorly understood. Frequently large cells are seen in the bone marrows of patients with CLL and evidence of RS. Using a laser-capture microdissection we analyzed small and large leukemic bone marrow cells from 19 patients with RS for loss of heterozygosity (LOH) on chromosome 11 (D11S2179 at the ATM gene), 17 (D17S938 and D17S1852 at the TP53 site), and 20 (Plc1, D20S96, D20S110, and D20S119). Megakaryocytes were also isolated and used as a control for normal cells. Four of 15 (27.7%) informative cases showed LOH in small cells in the ATM gene while seven (46.7%) showed LOH in large cells. Six of 15 (40%) informative cases had LOH in chromosome 17 in small cells, and eight (53%) showed LOH in large cells. Eleven of 19 informative cases (61.1%) showed LOH in chromosome 20 in large cells, and eight (42.1%) showed LOH in small cells. RS cases with LOH at chromosome 20 were associated with marginally shorter survival rates (P = 0.08). Our data suggest that there are significant molecular differences between large and small cells in patients with CLL. Further analysis of the genes on these chromosomes may provide new insight into our understanding of the transformation of small CLL cells to large (Richter) cells.

Different mechanisms lead to a karyotypically identical t(20;21) in myelodysplastic syndrome and in acute myelocytic leukemia

A new t(20;21)(q11;q11), associated with a deletion on the long arm of chromosome 20, was found in one patient with an acute myelocytic leukemia (AML) and in one with myelodysplastic syndrome (MDS). In both cases deletion was interstitial, extending from band q11 to band q13, as shown by comparative genomic hybridization (CGH) and fluorescence in situ hybridization (FISH). FISH analysis with whole arm paints, subtelomeric probes, and locus-specific probes for the long arms of chromosomes 20 and 21 revealed in patient 1 a reciprocal translocation between the deleted 20q and the long arm of chromosome 21, that is, del(20)(q11q13)t(20;21)(q11;q11), and in patient 2, material from 21q was inserted into the deleted 20q, that is, del(20)(q11q13)ins(20;21)(q11;q11q22). This is the first identification of a complex 20;21 rearrangement in MDS/AML. Deletion at 20q and juxtaposition between 20q11 and 21q11 appear to be the critical genomic events.

Identification of candidate genes on chromosome band 20q12 by physical mapping of translocation breakpoints found in myeloid leukemia cell lines

Deletions of the long arm of chromosome 20 have been reported in a wide range of myeloid disorders and may reflect loss of critical tumor suppressor gene(s). To identify such candidate genes, 65 human myeloid cell line DNAs were screened by polymerase chain reaction (PCR) for evidence of allelic loss at 39 highly polymorphic loci on the long arm of chromosome 20. A mono-allelic pattern was present in eight cell lines at multiple adjacent loci spanning the common deleted regions (CDRs) previously defined in primary hematological samples, suggesting loss of heterozygosity (LOH) at 20q. Fluorescence in situ hybridization (FISH) was then performed using a series of yeast artificial chromosomes (YACs) ordered in the CDR, and in five of eight cell lines, the deletions resulted from cytogenetically detectable whole chromosomal loss or large interstitial deletion, whereas in another cell line deletion was associated with an unbalanced translocation. LOH in the CMK megakaryocytic cell line, which has a hypotetraploid karyotype, was associated with a der(20)t(1;20)(q32;q12)x2 leading to complete deletion of the CDR. Three additional unbalanced translocations were found within the CDR and all three breakpoints mapped to a single YAC. We then used a series of P1 artificial chromosomes (PACs) spanning this YAC clone, and two PACs produced 'split' signals suggesting that they each span one of these breakpoints. Exon trapping using PACs that overlap the breakpoint regions yielded portions of six genes and evaluation of these genes as candidate tumor suppressor genes is underway. The limited information available about these genes suggests that the h-l(3)mbt gene is the most attractive candidate.

Complex chromosome 9, 20, and 22 rearrangements in acute lymphoblastic leukemia with duplication of BCR and ABL sequences

Cytogenetic analysis was performed on bone marrow cells from a 28-year-old woman who was diagnosed with acute lymphoblastic leukemia (ALL). Her karyotype was: 46,XX,t(9;22)(q34;q11)[6]/47, XX,+8,t(9;22)(q34;q11)[4]/47,XX,+8,t(9;22)(q34;q11),del(20)(q11)[2]/46, XX,t(9;22)(q34;q11),del[20](q11)[7]/45,XX,der(9)t(9;22)(q34;q11),-20,-22 , +mar1[8]/45,XX,der(9)t(9;22)(q34;q11),-20,-22,+mar2[3]. Both marker chromosomes are dicentric and have the same size and banding pattern but different primary constrictions. Fluorescence in situ hybridization (FISH) demonstrated that both markers were derived from chromosomes 9, 20, and 22. FISH with the bcr/abl probe showed fusion of the BCR gene with the ABL gene; however, this fusion signal was present in duplicate on both marker chromosomes. To our knowledge, duplication of the BCR/ABL fusion signal on a single chromosome arm has not been reported before, except for the extensive amplification of BCR/ABL fusion signals in the leukemic cell line K-562. These data demonstrate that the marker chromosomes are the result of complex genomic rearrangements. At the molecular level, the BCR/ABL fusion gene encodes the p190 fusion protein. Similar findings have never been observed in any case of ALL.