Page 939 - Hematology_ Basic Principles and Practice ( PDFDrive )

822 Part VII Hematologic Malignancies

trials for CLL. Moreover, a complex conventional karyotype remains
Genetic Testing for Acute Lymphoblastic Leukemia (ALL)
an independent prognostic indicator associated with a poor outcome.
At diagnosis, conventional cytogenetic studies should be performed, Chromosome abnormalities in CLL detected by FISH are of
especially for pediatric patients in whom solely numerical anomalies prognostic significance (Fig. 56.47). Four genomic aberrations, as
occur in 25%. FISH and molecular genetic methods are helpful in well as normal findings, are independent predictors of disease pro-
detecting certain cryptic chromosome anomalies, such as ETV6- gression and survival. Genomic aberrations of prognostic significance
RUNX1 fusion associated with t(12;21)(p12;q22). The panel of FISH include 17p deletion, 11q deletion, trisomy 12, and 13q deletion.
probes useful at the diagnosis of pediatric ALL include ETV6-RUNX1, Survival in these groups was 32, 79, 114, and 133 months, respec-
MLL, BCR-ABL1, TCF3/PBX1 and CDKN2A (9p21.3), and CDKN2B tively, and the treatment-free interval was 8, 12, 33, and 92 months,
(9p21.3) on the short arms of chromosome 9, and centromeric probes respectively (see Fig. 56.46). Survival of patients with a normal
for chromosomes 4, 10, and 17. In adults, the role of hyperdiploidy as karyotype was 111 months, and the treatment-free interval was 49
it relates to prognosis is uncertain; thus FISH testing with centromeric
probes is not useful. Establishing benchmarks with FISH and/or months. The deletion of 17p13 affects the tumor suppressor gene
molecular testing is crucial for follow-up of patients during and after TP53. In 80% to 90% of the cases, a deletion of 17p is associated
therapy. with mutated TP53 on the remaining copy. This is one possible
reason why p53 pathway–based therapies are not effective in patients
with 17p deletion. TP53 mutations have been found in 4% to 15%
of patients with early-stage CLL and are associated with poorer
than 1 year, the development of ALL occurs during fetal develop- outcome. Deletion of 11q and deletion of the ATM gene on 11q23.1
ment because they share a single placenta resulting in blood cell are found in 18% of patients with CLL. In about one-third of
chimerism. The prenatal mutation occurs commonly, exceeding the patients with deleted 11q, a simultaneous mutation of ATM has been
actual rate of developing leukemia by some 100-fold, indicating a found. The OS of these patients is shorter.
low rate of reentrance or evolution. The acquisition of the additional FISH-detected anomalies are frequent in B-CLL cases with Rai
genetic lesions, such as copy number alterations of ETV6, PAX5 stages 0 to 1 disease, but are more frequent among patients with
and CDKN2 (25%–75% of cases) are recurrent and contribute to progressive disease (88%) than in those with stable disease (66%).
leukemogenesis. After testing five pairs of monozygotic twins with Two risk groups have been recognized: (a) low risk disease includes
concordant ETV6-RUNX1–positive ALL, Greaves and his colleagues patients with a normal karyotype or isolated del(13q); (b) high risk
demonstrated that all recurrent driver mutations detected (32 in total) includes patients with del(11q) and del(17p). Patients with +12 are
were different within twin pairs, indicating that they are postnatal in high risk, but in contrast to del(11q) and del(17p), they respond to
origin in both twins and most likely represent secondary mutations. fludarabine-based therapies (see Fig. 56.46). A comparison of quan-
Further single cell analyses revealed considerable complexity within a titative PCR method with FISH for assessment of the four most
tree-like or branching structure of genetically distinct subclones, and frequent aneuploidies revealed a tight correlation in 103 of 110
as Greaves and colleagues suggested, very reminiscent of Darwin’s patients examined, with FISH being more sensitive in detecting
original 1837 evolutionary divergence diagram (see box on Genetic subclonal genetic evolution.
Testing for Acute Lymphoblastic Leukemia, and earlier section on The frequency of chromosome 13 abnormalities in CLL detected
clonal origin). by conventional cytogenetics is 10% to 15%. However, with the use
of FISH, smaller or larger deletions of band q14.3 are detected in up
to 60% of patients over time. When multiple DNA probes are used,
B-CELL CHRONIC LYMPHOCYTIC LEUKEMIA D13S319 and D13S25 DNA markers are deleted more frequently
than is RB1. Molecular analyses have detected deletions of 13q in
Historically, classic metaphase cytogenetic analyses of CLL were cells that are cytogenetically normal as well as abnormal. These dele-
difficult because of the low mitotic yield of neoplastic B cells despite tions can either be heterozygous (76%) or homozygous (24%).
the use of polyclonal B-cell mitogens. FISH analysis of nondividing Heterozygous deletions most frequently occur in the early stage of
interphase cells was applied for the first time to hematologic malig- the disease and homozygous deletions occur in the more advanced
nancy, for the risk stratification of CLL. Introduced in 2000 by stages. In a study examining loss of heterozygosity and subchromo-
Dohner, the FISH hierarchical prognostic model stratifies patients somal copy losses of chromosome 13, two types of deletions were
into good [normal cytogenetics, del(13q)], intermediate with trisomy defined: type 1 aberrations occurred in 60% of cases and were associ-
12, and poor prognostic groups [del(11q) and del(17p)] and remains ated with loss of Rb1 and breaks close to the miR16/15a locus; and
26
the most accepted and validated genomic prognostic model. More- type 2 aberrations that included Rb1 occurred in 40% of cases. The
over, current guidelines still recommend FISH analysis before treat- 13q14.3-deleted segment contains micro-RNA (miRNA) genes.
ment initiation and also following relapse or lack of response to miRNAs are normally made by cells, including B lymphocytes, and
therapy. they regulate the function of many genes. All patients with homozy-
Cytogenetically CLL is characterized by relatively stable genome gous 13q deletion have a dramatic downregulation of miRNA15a,
with a gain or loss of chromosomal regions; balanced translocations, whereas patients with hemizygous 13q deletions are indistinguishable
a hallmark of AML, are rare in CLL. With improved detection rate from controls, providing the first molecular clues for pathogenesis of
of aberrant karyotypes in CLL using cultivation with CD40 ligand CLL. The percentage of CLL cells with del(13q) is predictive of
(DSP30) and interleukin 4 and the application of molecular cytoge- survival: a high percentage (>80%) of del(13q) cells results in a
netics, such as FISH, aCGH, as well as NGS, the detection rate of shorter survival as compared with patients with a lower percentage
genomic changes has been raised to 80% to 90%. Analysis of clini- (<80%) of del(13q) cells. The clinical correlation with del(13q) cells
cally relevant chromosomal loci, combined with immunophenotyp- include a higher lymphocyte count, a tendency to exhibit a diffuse
ing, mutational analyses of the Ig heavy-chain variable region (IgV H ), pattern of bone marrow infiltration, and splenomegaly. Trisomy 12
and ZAP-70 overexpression, are of prognostic importance, even or 13q rearrangements are found separately in a substantial propor-
though the oncogenic events that lead to the origin of B-CLL remain tion of patients with CLL. They co-exist in only 2% to 5% of
unknown (Tables 56.11 and 56.12 and Fig. 56.46; see also box on patients, suggesting that each change may have a distinct pathogenetic
Genetic Testing for B-Cell Chronic Lymphocytic Leukemia). route. The presence of del(13q) as the sole abnormality in CLL is
Although microarray and high-density SNP array studies have not associated with the most favorable prognosis, with a median survival
identified genes involved in the pathogenesis of CLL, they are helpful of 11 years.
in clarifying the heterogeneous nature of CLL, which is a single Among the first-degree relatives of patients, population studies
disease entity with a common genetic phenotype resembling memory have demonstrated a sevenfold increased risk for developing CLL and
B lymphocytes. Genetic testing is strongly recommended for all a twofold increased risk for developing other lymphoproliferative
patients with CLL, particularly in the context of novel therapeutic disorders. More than 80 families with CLL affecting multiple family