Haematologica 2003 - Supplements

P2.5
MOLECULAR CYTOGENETICS OF MYELOMA
BIOLOGY: CLINICAL AND PROGNOSTIC
IMPLICATIONS
Rafael Fonseca, and Philip R Greipp
Hematology and Internal Medicine, Mayo Clinic, Rochester, MN,
55905
1. INTRODUCTION: Cytogenetic and genetic abnormalities are
thought to be critical for the pathogenesis of multiple myeloma
(MM). We have embarked on the study of genetic abnormalities
in MM to better understand their relationship to pathogenesis and
clinical outcome. We have studied these abnormalities using a
combination of classical molecular techniques, molecular
cytogenetics (cIg-FISH), conventional karyotype analysis and
novel genomic platforms (gene expression analysis). We have
carefully considered the implications of specific chromosome
abnormalities for a) the different stages of the disease, and b)
evidence of ongoing genomic evolution and heterogeneity.
2. IgH TRANSLOCATIONS: The work done by several groups has
now revealed that IgH translocations, mostly occurring at the
time of isotype class switching, are present in the majority of
patients with MM (~60%). They appear to be early genetic
(clone initiating?) events since they are observed since MGUS.
Additional evidence suggest that IgH translocations may
represent the immortalizing event for the clone; their biologic
plausibility, upregulation of oncogenes, presence in other B-cell
neoplasms, initiated by B-cell specific recombination, clonally
selected and most recently associated with dissimilar clinical
outcomes. We have recently found that with serial evaluation
IgH translocations are always conserved, and that with
development of human MM cell lines and extramedullary MM,
gaining extra copies of the derivative chromosomes seem to be
advantageous for clonal expansion.
3. CLINICAL IMPLICATIONS FOR THE IgH TRANSLOCATIONS: Our
group and others have now shown that the different IgH
translocations have a significant impact on the ultimate outcome
of patients; patients with the t(4;14)(p16.3;q32) and with
t(14;16)(q32;q23) have very aggressive disease and have shorter
survival. In contrast, patients with t(11;14)(q13;q32) seem to
have a better prognosis. These effects on patients’ outcome seem
to be influenced by treatment modality administered; for instance
high-dose chemotherapy seems to provide greater benefit for
patients with the t(11;14)(q13;q32). In contrast it appears that
high dose therapy does not provide much benefit for patients with
the more aggressive IgH translocations. These observations
suggest that MM maybe composed, much like AML, of subgroups
of patients categorized by the specific IgH translocations.
While the relative effect on overall prognosis of IgH
translocations would seem to comparable to that of the most
robust prognostic variables, determining their presence will be of
even greater importance for the development of targeted
therapies.
4. ANEUPLOIDY: Aneuploidy as a category is the single most
common abnormality in MM. Aneuploidy in MM at first glance
appears to be random, but detailed studies of abnormal
karyotypes have now shown that not to be the case. While
numerical abnormalities are seen in the vast majority of patients,
monosomies are seen in nearly all karyotypes while trisomies are
only seen in 50% of patients. The chromosomes involved
trisomies and monosomies are not random; trisomies
predominantly involve chromosomes 3, 5, 7, 9, 11, 15, and 19,
and monosomies involve chromosomes 8, 13, 14, 16 and 22.
5. HYPERDIPLOID AND NON-HYPERDIPLOID MM: Based on the
presence of numerical abnormalities alone four sub-categories of
MM are discernible; hypodiploid; pseudo-diploid, hyperdiploid
and near tetraploid. Because of the extreme similarities between
the hypo-, pseudo- and tetraploid karyotypes we have proposed
the classification of MM into two major subtypes; hyperdiploid
and non-hyperdiploid MM. This classification is highly relevant,
as it has been recently shown that there is a marked difference in
the prevalence of IgH translocations between the two groups;
high in the non-hyperdiploid MM and low in the hyperdiploid
MM. The striking association has suggested that two major
pathways may be possible for MM pathogenesis; one that is
initiated by IgH translocations and one that is initiated by a yet to
be identified mechanism and whose end result is hyperdiploidy.
It appears the same associations are present since MGUS but
further work is needed to address these fundamental observations
of disease pathogenesis. While the aforementioned studies were
based on data derived form the study of abnormal karyotypes, the
same observations are seen, and in the same degree when ones
studies patients samples with FISH probes or via DNA content by
flow. Hypodiploid MM is associated with a very poor prognosis,
short survival and low response to treatment. Non-hyperdiploid
MM seems to provide a proliferative advantage to the clone such
that it emancipates the cells from the bone marrow and allows for
the growth of cells in extramedullary sites. In fact, all human MM
cell lines derive from the non-hyperdiploid MM and new models
for the ex-vivo study of hyperdiploid MM are needed (e.g. mouse
passage of hyperdiploid MM cells).
6. CHROMOSOME 13 DELETION/MONOSOMY: Loss of chromosome
13, both deletion of 13q14 and monosomy, (∆13) have emerged
over the last decade as a prominent prognostic cytogenetic
factors. The negative prognostic associations are observed
whether ∆13 are detected by karyotype analysis or by FISH. ∆13
detected by karyotype identify a group of patients with a grave
prognosis, and more commonly hypodiploid. Observing ∆13 via
karyotype is of course including the negative prognostic
implications of obtaining any abnormal metaphase (proliferation)
plus the negative biologic implications of having ∆13. In contrast
∆13 detected by FISH identifies a group of patients with the
biologic abnormality. Several features suggest ∆13 are important
(and not simply a marker) for pathogenesis; recurrent nature,
clonally selected, effect on prognosis and the lack of trisomy 13.
However, there is no specific gene identified as importantly
associated with the loss yet. In addition it is not clear whether
∆13 is merely a surrogate marker of hypodiploid variant MM.
Hypodiploid MM is associated with a high incidence of
aggressive IgH translocations (e.g. t(4;14)(p16.3;q32)) and with
an extremely poor prognosis. In fact we have recently shown that
many other monosomies may also be associated with a
significantly shorter survival. Much like IgH translocations we
also observed ∆13 in a similar fraction of MGUS patients
7. STAGES OF THE DISEASE: The current available information does
not allow full elucidation of genomic aberrations that are seen in
MM but not in MGUS. While differences still exist with regards
to the prevalence of specific lesions (e.g. ∆13 or
t(4;14)(p16.3;q32)), all cytogenetic features seen in MM have
been described as well in MGUS by FISH. The only two
abnormalities that are consistently reported as lower in
prevalence in MGUS, and present in a sizable fraction of MM,
are ras mutations and p16 gene silencing by methylation. In
contrast other abnormalities seem to be increasingly common
with advancing stages of the disease; c-myc abnormalities, p53
inactivation and secondary translocations.
8. GLOBAL INTEGRATION OF GENETICS, CYTOGENETICS AND GENE
EXPRESSION PROFILING: As more information has emerged with
regards to the genetic nature of MM, it has become increasingly
S24