Keywords
plasma cell dyscrasia - multiple myeloma - FISH - MGUS - SMM - plasma cell leukemia
- cytogenetics in myeloma
Introduction
Plasma cell dyscrasias are a group of heterogeneous neoplasms characterized by clonal
proliferation of plasma cells. Based on the percentage of plasma cell infiltration
in the bone marrow, the type of monoclonal protein, association of CRAB (hypercalcemia,
renal impairment, anemia, or lytic bone lesions) plasma cell dyscrasias are classified
as[1]
[2]:
-
IgM monoclonal gammopathy of undetermined significance
-
Non IgM monoclonal gammopathy of undetermined significance
-
Smoldering (asymptomatic) plasma cell myeloma
-
Multiple myeloma (plasma cell myeloma):
-
➢ Multiple myeloma NOS
-
➢ Multiple myeloma with recurrent genetic abnormality
-
➢ Multiple myeloma with CCND family translocation
-
➢ Multiple myeloma with MAF family translocation
-
➢ Multiple myeloma with NSD2 family translocation
-
➢ Multiple myeloma with hyperdiploidy
-
Solitary plasmacytoma of bone
-
Extraosseous plasmacytoma
-
Monoclonal immunoglobulin deposition disease
-
Immunoglobulin light chain amyloidosis (AL)
-
Localized AL amyloidosis
-
Light chain and heavy chain deposition disease
The plasma cells undergo several rounds of differentiation in the bone marrow and
secondary lymphoid organs and involve V(D)J rearrangements and somatic hypermutation
with class switch recombination.[3] Sentinel chromosomal abnormalities acquired in the process of maturation and differentiation
result in neoplastic transformation of the plasma cells.[3] These cytogenetic abnormalities are integral to risk stratified treatment protocols.
The founding or primary chromosomal abnormalities that occur early in the course of
the disease are IgH gene rearrangements and aneuploidy.[3]
[4] Secondary chromosomal abnormalities are either acquired or enriched at disease progression
and include deletion of short arm of chromosome 17 (deletion 17p/TP53), deletion of short arm of chromosome 1 (1p deletion), gain or amplification of long
arm of chromosome 1 (1q gain/amp), deletion of long arm of chromosome 13 (13q deletion)
and MYC gene rearrangements.[4]
In IgH gene rearrangements, the promoter sequences of the IgH enhancers cause overexpression of the partner genes. The recurrent IgH translocations in multiple myeloma (MM), involve CCND1 at 11q13, CCND3 at 6p21, FGFR3/MMSET/CCND2 at 4p16 resulting in increased expression of cyclin D family of genes that promote
cell cycle progression and increased proliferation. IgH translocations involving the MAF family of genes include MAF at 16q23 and MAFB at 20q11, resulting in the upregulation of MAF-associated transcription process.[5]
Aneuploidies include hyperdiploid MM and the non-hyperdiploid MM. Hyperdiploidy in
plasma cells neoplasms is characterized by nonrandom gains of chromosomes 3, 5, 7,
9, 11, 15, 19, and 21. The gains of chromosomes result in gene dosage effects, altering
gene expression. Gains of chromosome 11 is associated with the overexpression of the
CCND1 gene. Nonhyperdiploid MM includes hypodiploid (<45 chromosomes) and pseudodiploid
(45–46 chromosomes).[5]
[6]
Secondary cytogenetic abnormalities can be present either at diagnosis or may be enriched
or acquired during progression of the disease. The molecular mechanisms that promote
progression include the activation of the RAS pathway and MYC overexpression accompanied by DNA hypomethylation leading to genomic instability
([Fig. 1]).
Fig. 1 Cytogenetic and genetic abnormalities occurring in the evolution of plasma cell dyscrasias.
In this review, we will focus on the role of cytogenetics for the work up of plasma
cell dyscrasias.
Cytogenetic Risk Stratification
MM is a heterogeneous disease characterized by multiple genetic subtypes that have
varied response to treatment and are an integral component of risk stratification
of the disease. The impact of cytogenetic abnormalities on time to progression (TTP)
varies according to the type of plasma cell dyscrasia. In MM, the standard risk abnormalities
include t(11;14), t(6;14), and hyperdiploidy (gains of 3/5/7/9/11/15/19 and or 21)
and high-risk abnormalities include t(4;14), t(14;16), t(14;20), deletion of short
arm of chromosome 17 (Del 17p), gain or amplification of long arm of chromosome 1
(1q gain/amp), deletion of short arm of chromosome 1 (1p deletion), MYC gene rearrangements, and deletion of long arm of chromosome 13 (13q deletion).[1]
[2]
[7]
[8]
The revised international staging system for myeloma established by the International
Myeloma Working Group includes high-risk cytogenetic abnormalities such as t(4;14),
t(14;16) deletion 17p/TP53 along with serum albumin, serum β-2 microglobulin, and serum lactate dehydrogenase
levels. The second revision of the RISS excluded t(14;16) and included 1q amplification
in the scoring system.[9]
The Mayo Clinic includes both the standard risk and high-risk cytogenetic abnormalities
in the Stratification for Myeloma and Risk Adapted Therapy (mSMART) protocol ([Table 1]).[10]
[11]
[12]
[13]
Table 1
mSMART 3.0 criteria for risk stratification of active multiple myeloma
|
mSMART 3.0
(risk stratification of active MM)
|
|
Standard risk
|
High risk [a]
[b]
|
|
Trisomies of 3/5/7/9/11/15/19 and or 21*
|
t(4;14)
|
|
t(11;14) [d]
|
t(14;16)
|
|
t(6;14)
|
t(14;20)
|
|
Del 17p
|
|
TP53 mutation
|
|
1q gain
|
|
• R-ISS stage 3
• High-plasma cell S-phase[c]
• GEP: High-risk signature
|
|
Double-hit myeloma: any 2 high-risk abnormalities
|
|
Triple-hit myeloma: ≥3 high-risk abnormalities
|
a Trisomies may ameliorate.
b By FISH or equivalent method.
c Cutoffs vary.
d t(11;14) may be associated with plasma cell leukemia.
Double-Hit and Triple-Hit Myeloma
The mSMART 3.0 proposed by the Mayo Clinic has proposed a concept of double-hit myeloma
and triple-hit myeloma similar to the concept seen in lymphomas.[14] These are defined as follows:
High-risk abnormalities include deletion 17p/TP53, 1q gain/amp, t(4;14), t(14;16), t(14;20)
Double-hit MM (DH-MM) includes any two high-risk abnormalities
Triple-hit MM (TH-MM) includes three or more high-risk abnormalities
These are considered as the 'ultra-high risk' abnormalities showing rapid disease
progression and shorter overall survival as compared to MM having a single or no high-risk
abnormality. The most common high-risk abnormalities seen were 1q gain/amp, t(4;14),
deletion 17p/TP53 in several studies.[15]
[16]
Cytogenetic Lab Approach in MM
The cytogenetic strategy in plasma cell dyscrasia is based predominantly on FISH analysis
of neoplastic plasma cells. The use of karyotyping has decreased in recent years due
to reasons explained below. Although single nucleotide polymorphism (SNP) array has
been used to identify copy number abnormalities, it does not identify fusions and
the results have to be integrated with FISH analysis.[17]
[18]
Transcriptomic analysis has been used to identify high-risk gene expression signatures.[19]
[20] This review will focus on FISH-based approach to identify the genetic subtypes.
Karyotyping (Conventional Cytogenetics)
Karyotyping relies on the ability of plasma cells to divide, which is limited, making
it difficult to acquire metaphases for study. Stimulants such as lipopolysaccharide
(LPS), 12-O-tetradecanoylphorbol-13-acetate (TPA or phorbol 12-myristate 13-acetate),
and cytokines (interleukin-6 and granulocyte–macrophage colony-stimulating are used
to increase the yield of metaphases, their role in IgM-negative B cells being limited.[21]
[22] Oligonucleotides containing CpG motif, such as synthetic DSP30, can stimulate cells
of the immune system in vitro and hence can be used to increase the yield of metaphases
in vitro.[23] Various cytokines such as IL-10, IL-2, and TNF-alpha can also be used as mitogens
for increasing the yield of metaphases.[23] Though G-banded analysis has the advantage of whole genome analysis at a low resolution
([Fig. 2A]), low or no yield of metaphases from the plasma cells limits its utility in identifying
the subtypes. Karyotyping fails to identify cryptic translocations involving the IgH locus such as t(4;14) and t(14;16) and a subset of cryptic 17p deletions. Hence,
FISH is a superior tool with better sensitivity and specificity in identifying the
clinically relevant genetic subtypes.[17]
[24]
Fig. 2 (A) GTG banded karyotype image showing hyperdiploidy with deletion of long arm of chromosome
6 and a balanced translocation between the long arms of chromosome of 8 and 22. (B) Interphase FISH with IgH break-apart probe positive for IgH rearrangement. (C) Interphase FISH with CCND1::IgH dual color dual fusion probe positive for t(11;14). (D) Interphase FISH with LSI D5S23, D5S721/CEP 9/CEP 15 tricolor probe depicting trisomies
for chromosomes 5,9,15. (E) Interphase FISH with 1p(CDKN2C)/1q(CKS1B) LSI probe depicting deletion of 1p(CDKN2C) and gain of 1q(CKS1B). (F) Interphase FISH targetingTP53 gene depicting TP53 deletion.
Fig. 3 Magnetic cell sorting (MACS) of CD138+ plasma cells using anti-CD138 and anti-dextran
complex through positive selection of plasma cells in a magnetic chamber.
Fluorescent in-situ Hybridization
FISH does not require live cells and can be performed on interphase cells. Plasma
cell infiltration of the bone marrow can be patchy in MM, and the percentage of plasma
cells in the marrow may vary. It is essential to enrich plasma cells before application
of probes and performing the FISH analysis. Currently, FISH is the preferred tool
to identify the genetic subtypes for risk stratification in MM patients.[24]
[25]
[26]
[27]
Various Plasma Cell Enrichment Techniques
Various Plasma Cell Enrichment Techniques
-
1) Magnetic cell sorting (MACS)
-
2) Fluorescence activating cell sorting (FACS)
-
3) Targeted manual sorting
-
4) Customized automated image analysis
-
5) Cytoplasmic immunoglobulin FISH (cIg-FISH)
-
6) Target FISH[28]
Magnetic Cell Sorting
The adhesion of the plasma cells to an antibody cocktail serves as a basic principle
for sorting the cells. Fresh heparin bone marrow samples are treated with an anti-CD138
and anti-dextran antibody complex. Magnetic beads are added that bind to the dextran
complex and this is subjected to a magnetic chamber for separation. The unbound particles
are washed off and the mixture obtained contains the sorted plasma cells ([Fig. 3]). The technique is cost-effective and requires fresh samples, as the yield decreases
with the age of the sample.[28]
Fluorescence Activating Cell Sorting
Fluorescence Activating Cell Sorting
Flow cytometric sorting of neoplastic plasma cells is performed using a cocktail of
various antibodies (e.g., anti-CD45, anti-CD56, and anti-CD38) along with assessment
of light scattering ability of plasma cells. FACS is more efficient than MACS as it
uses multiple antibodies and parameters to identify and sort neoplastic plasma cells,
thereby increasing the yield of plasma cells available for characterization. Higher
capital and maintenance costs and restricted access coupled with cost of monoclonal
antibodies have limited the use of sorter in most of the routine diagnostic laboratories.[28]
[29]
Targeted Manual Sorting
Targeted manual sorting relies on morphological identification of large mononuclear
cells. One of the limitations of Target FISH is the intensity of signals that is weak
and not uniform across the slide. The technique is subjective, requires skilled manpower,
is time consuming with an increase possibility of false-negative results.[28]
Customized Automated Image Analysis
Customized Automated Image Analysis
FISH slides are subjected to automated slide scanning where the mono nuclear cells
are identified using a software classifier. The ability to count more cells increases
the sensitivity of this technique as compared to manual analysis. The major drawback
is the capital costs and infrastructure required to store and analyze the images.[28]
Cytoplasmic Immunoglobulin
Cytoplasmic Immunoglobulin
Plasma cells are differentiated from other cells in the marrow by staining them with
anti-kappa or anti-lambda antibodies (cytoplasmic immunoglobulin FISH [clg-FISH]).
The method is tedious, requires additional time for careful meticulous examination
of the slides. In cases with aggregation of small plasma cells, the analysis is difficult.
The modified cIg FISH has refined the identification of plasma cells by fixing the
plasma cells to avoid clumping or aggregation by replacing 96% ethanol wash with 100%
methanol. The method is the preferred technique of FISH on plasma cells in a large
number of laboratories.[30]
[31]
[32]
Target FISH
Plasma cells are sorted by centrifugation using Ficoll and are then stained with May–Grünwald
Giemsa (MGG) stain. Plasma cells are identified based on morphology and are captured
using an automated system. These slides are then de-stained and FISH is performed
on the same slides. Plasma cells are identified based on the analysis of previously
captured and analyzed images and FISH signals are recorded on the same cell. The disadvantage
is that thousands of images are captured and there are reports of discordant results
between the images captured.[33]
Quantitative Multigene Fluorescent in-situ Hybridization
Quantitative Multigene Fluorescent in-situ Hybridization
Quantitative multigene fluorescent in-situ hybridization (QM-FISH) is a cytological
high-resolution technique used to identify heterogeneity and clonal evolution in cases
of MM. Single cell analysis could provide new insights into the clonal evolution in
MM. Because MM is a heterogenous disease, clonal evolution is a continuous process
and QM-FISH can only identify selective abnormalities. QM-FISH could prove to be an
important tool to analyze the new emerging clones with its sensitivity being similar
to conventional FISH.[34]
Quantitative multigene fluorescent in-situ hybridization (QM-FISH) is a cytological
high-resolution technique used to identify heterogeneity and clonal evolution in cases
of MM. Single cell analysis could provide new insights into the clonal evolution in
MM. Because MM is a heterogenous disease, clonal evolution is a continuous process
and QM-FISH can only identify selective abnormalities. QM-FISH could prove to be an
important tool to analyze the new emerging clones with its sensitivity being similar
to conventional FISH.[34]
Pre-analytical Variables and Quality Control
Pre-analytical Variables and Quality Control
The first pull bone marrow aspirate sample is the preferred sample for cytogenetic
studies in MM. The sample should be transported as soon as possible to the laboratory
and processed with minimum delay. A delay in the transport and processing of samples
results in the depletion of the plasma cells impacting the results of the study. Hemolyzed
and clotted samples adversely impact the plasma cell enrichment process and a repeat
sample should be requested. While standardizing the plasma cell enrichment process
using MACS, flow cytometry-based analysis should be performed to evaluate the efficiency
of the enrichment process to positively select the CD138-positive plasma cells. The
laboratory should perform analysis on known positive and negative samples to calculate
the cut-off for each probe. A recommendation of 10% for fusion or break-apart probes
and 20% for numerical abnormalities has been mentioned in some studies.[35]
These recommendations are not universally accepted and ideally the laboratories should
define their own cut-off values for each probe. It is expected that in samples with
plasma cell enrichment the primary abnormalities will be present in the majority of
the cells as compared to the secondary abnormalities. Ideally, 100 cells should be
evaluated by at least two analysts.[35] Cut-off values for each probe can be calculated by either using CV with standard
deviation and beta inverse function or using the Excel (Microsoft, Redmond, WA) statistical
function CRITBINOM (n, p, α) with a confidence level of 95%.[36]
FISH studies on bone marrow biopsies are technically challenging with high frequency
of failure due to the use of acids in decalcification process. Fixation in 10% neutral
buffered formalin for at least 24 hours and EDTA-based decalcification are recommended
for optimal FISH analysis on bone marrow biopsy specimens. In patients, showing patchy
interstitial infiltration by plasma cells in the bone marrow biopsy, identifying the
plasma cells is challenging and essential expertise is required to avoid false-negative
results.
Probe Selection
To identify deletions/amplifications dual-color locus specific probes with an internal
control is recommended. A break-apart probe is used for identifying IgH and MYC rearrangements. Dual color fusion probes are used to identify specific IgH partners.[35]
[37]
Step Wise FISH Strategy
FISH analysis to identify the clinically relevant genetic subtypes is performed in
a stepwise manner to judiciously utilize the enriched plasma cells and save costs
([Table 2]). The first step involves testing for 17p,13q deletion, 1q gain/1p deletion, IgH and MYC rearrangement using respective break-apart probes and centromeric probes targeting
5,9,15 to identify trisomies. Based on the results of the initial panel, patient samples
positive for IgH rearrangement ([Fig. 2B]) are reflex tested using specific fusion probes to identify the partner. Follow-up
samples are tested for deletion 17p, MYC rearrangements, and 1q gain/amp.
Table 2
Stepwise FISH strategy in multiple myeloma
|
At diagnosis
|
|
IgH gene rearrangement
|
|
Deletion 17p
|
|
1q gain/amplification
|
|
1p deletion
|
|
8q24.1 rearrangement, MYC break apart
|
|
Deletion 13q
|
|
CEP 5/9/15 (By FISH or flow ploidy)
|
|
If positive for IGH gene rearrangement
|
|
t(11;14)(q13;q32), CCND1::IgH fusion
|
|
t(6;14)(p21;q32) CCND3::IgH fusion
|
|
t(4;14)(p16.3;q32) FGFR3::IgH fusion
|
|
t(14;16)(q32;q23) IgH::MAF fusion
|
|
t(14;20)(q32;q12) IgH::MAFB fusion
|
|
At follow-up
|
|
Deletion 17p
|
|
1q gain/amplification
|
|
8q24.1 rearrangement, MYC break apart
|
Subtypes Based on Genetic Abnormalities
IgH Rearrangements
IgH rearrangements occur early in the course of the disease. The rearrangements result
in over expression of the partner gene due to the impact of enhancer elements in the
promoter regions of the IgH gene.[38] The IgH rearrangements based on the partner gene can be sub grouped as
IgH Rearrangements with CCND Family: t(11;14) and t(6;14)
Translocations involving the CCND family of genes are associated with standard risk as per the mSMART criteria. t(11;14)(q13;q32)
involves the CCND1 gene ([Fig. 2C]) and is seen in 15-20% of patients, while t(6;14) (p21;q32) involves the CCND3 gene and is seen in < 5% of patients. The translocations cause dysregulation in cyclin
D, resulting in the RB1 gene inactivation leading to cell cycle progression.[5]
[6]
[39]
[40] Patients with t(11;14) also show overexpression of BCL2 and are known to benefit from therapy with Venetoclax (BCL2 inhibitor).[41]
[42] Though t(11;14) is associated with standard risk it has been reported in cases of
primary plasma cell leukemias and in association with MYC rearrangements.[43]
[44]
IgH Rearrangements with MAF Family Translocation
Translocations t(14;16)(q32;q23) and t(14;20)(q32;q11) are seen in < 3% and < 1%,
respectively, are associated with high risk. These upregulate the MAF family of genes, thereby activating the transcription by overexpression of CCND2.[5]
[6]
[40]
IgH Rearrangements with NSD2 Translocation
Translocation t(4;14)(p16;q32) is seen in 15% of the cases and is associated with
high risk. It causes the overexpression of FGFR3 (fibroblast growth factor receptor 3) and NSD2 (nuclear receptor binding SET domain protein 2), the latter also known as MMSET (multiple myeloma SET domain protein). FGFR3 plays an essential role in regulating cell proliferation, differentiation, and apoptosis.
The majority cases of t(4;14) show the overexpression of CCND2, a cell cycle regulator, though the exact mechanism is not understood.[5]
[6]
Aneuploidy
Aneuploidies are recurrent cytogenetic subtypes in MM and can be categorized into
hyperdiploid and nonhyperdiploid groups.
Hyperdiploidy
Hyperdiploidy (>46 up to 75 chromosomes) is associated with standard risk and is seen
in ∼55% of patients. It is characterized by non-random gain of chromosomes 3/5/7/9/11/15/19
and or 21 ([Fig. 2D]). Studies have shown that trisomy 3 and trisomy 5 are associated with a better overall
survival (OS), whereas trisomy 21 is associated with a poor OS.[45]
[46] The diagnosis of hyperdiploid MM is based on the presence of at least gains of two
or more chromosomes in the absence of any monosomies on FISH analysis.[47]
The non-hyperdiploid MM group includes hypodiploidy (<45 chromosomes) and pseudodiploidy
(45–46 chromosomes). The most common monosomies seen are for chromosomes 13, 14, 16,
and 22. This group is associated with a poor prognosis.[6]
[48]
Chromosome 1 Abnormalities
1q Gain/amplification
Gain/amplification of long arm of chromosome 1 (1q21) is seen in 28 to 44% cases of
MM. It is a secondary abnormality acquired during progression of disease. The copy
number gain of 1q21 (+1q21) is subclassified into gains (3 copies) and amplification
(≥4 copies). Prognostically, 1q21 amplification is associated with a worse overall
survival as compared to gain of 1q21[49] ([Fig. 2E]). Over expression of CKS1B was initially thought as the driver event, but later multiple genes such as MUC1, MCL1, ANP32E, BCL9, PSMD4, PDZK1, NEK2, ARNT, ILF2, and ADAR1 have been known to play a role in progression.[49]
[50]
[51]
[52]
[53]
[54] Jumping translocations involving 1q is another known mechanism that results in gains
of 1q.[53] The gain of 1q21 is considered as high risk as per the mSMART v 3.0 criteria and
has been incorporated into the second revision of RISS.[9]
1p Deletion
Deletion of short arm of chromosome 1 is seen in 18 to 38% of patients and is associated
with poor outcomes. The recurrent deletions are seen at loci 1p22 and 1p32 ([Fig. 2E]). While deletions involving the locus 1p22 have not shown significant impact on
survival, deletions involving the locus 1p32 (houses genes CDKN2C and FAF1) are associated with t(4;14), deletion 17p/TP53 and 13q deletion. Some studies have suggested deletion of 1p32 as an independent
prognostic risk factor with a high risk for relapse and early death.[55]
[56]
[57]
Deletion 17p/TP53
Deletion 17p/TP53 is associated with high-risk disease and can be acquired or enriched on disease progression[58] ([Fig. 2F]). The bi-allelic inactivation of the TP53 gene is a marker of 'ultra-high risk disease.'[59] Recently, this entity has also been included as a criteria for double/triple-hit
myeloma.[13]
Chromosome 13
Monosomy 13 and large deletions on long arm of chromosome 13 are established recurrent
cytogenetic abnormalities in MM, resulting in deletion of the RB1 gene. The size of the deletions varies and a commonly deleted region of pathogenic
significance has not been clearly defined. Previous studies have inferred that poor
prognosis in 13q deletions is associated with large deletions/monosomy 13 identified
on karyotype rather than smaller deletions identified on FISH only. [60] However, the observation was not consistent in subsequent studies and it is now
known that adverse prognosis in 13q deletions is more due to its association with
other high-risk markers such as t(4;14) and deletion 17p/TP53. [6]
Role of MYC
MYC translocations are seen in 13 to 15% of newly diagnosed or relapsed cases of MM.
These are commonly associated with older age group, plasmablastic morphology, hypercalcemia,
1q amplifications, and a poor outcome.[61]
[62]
[63] PARP1 inhibitors have been suggested as a therapeutic option in patients with MYC rearrangements based on the evidence that MYC acts as a promoter of PARP1 mediated repair in MM.[64]
MYC gene rearrangements involving the enhancer elements of the kappa and lambda light
chain genes, i.e., t(8;22)(q24;q11) and t(2;8)(p12;q24) are rare and are associated
with light chain type of monoclonal gammopathy[65]([Fig. 2A]).
Data from India on Frequencies of Cytogenetic Abnormalities
There are a few studies on cytogenetic characterization of myeloma patients from India,
one of the largest one describes the frequency of cytogenetic abnormalities in 475
patients identified on FISH analysis on enriched plasma cells. The study reported
abnormalities in 66% of patients with high-risk abnormalities in 52% of patients.
The study also reported smaller clonal size of secondary abnormalities compared to
primary abnormalities. The frequency of t(4;14) was reported to be higher than t(11;14).[37]
Role of FISH in Other Plasma Cell Dyscrasias
Monoclonal Gammopathy of Undetermined Significance (MGUS)
MGUS is characterized by the presence of serum monoclonal protein < 3 g/dL and the
bone marrow shows < 10% PCs and have a 1% per year risk of progression to MM.[19]
[66]
Deletion 17p/TP53, t(4;14), and trisomies are associated with a shorter time to progression (TTP) as
compared to the other cytogenetic markers in MGUS. In these patients, it was suggested
that trisomies may be an indicator of genomic instability, hence resulting in shorter
TTP.[67]
Smoldering Multiple Myeloma (SMM)
SMM represents a stage between MGUS and MM and is characterized by a serum monoclonal
protein ≥ 3 g/dL, bone marrow PCs ≥ 10% without CRAB features (hypercalcemia, renal
impairment, anemia, or lytic bone lesions). The risk of progression to MM is 10%,
3%, and 1% per year during the first 5 years, next 5 years, and subsequent 10 years
after diagnosis respectively.[68] In a large study with cytogenetic data available in 689 SMM patients t(4;14), t(14;16),
+1q, 13q deletion/monosomy 13q and deletion 17p/TP53 were associated with a shorter probability of progression at 2 years.[69] In other studies, the presence of t(4;14), deletion 17p/TP53, and 1q gain/amp were found to be associated with shorter TTP.[70]
[71]
Plasma Cell Leukemia
Plasma cell leukemia (PCL) is an aggressive form of plasma cell dyscrasia and can
present as de novo primary PCL (pPCL) or can be derived from a pre-existing plasma
cell dyscrasia, as a secondary PCL(sPCL). In PCL IgH translocations, deletion 17p/TP53, 1q gain/amp, and MYC gene rearrangements are associated with a high risk. pPCL is frequently associated
with t(11;14) and sPCL with t(4;14).[72] Translocation t(11;14) a standard risk marker in MM is associated with an aggressive
course in patients of pPCL.[72]
[73]
[74] The two genes reported to be involved in t(11;14) are CCND1 and MYEOV. MYEOV is not commonly seen involved in MM patients.[75]
Summary
Plasma cell neoplasms are characterized by primary founding chromosomal abnormalities
that includes IgH translocations and aneuploidies. Secondary abnormalities acquired at a later stage of the disease
evolution includes 17p/13q deletions, 1q gain/amp,1p deletion and MYC rearrangements.
FISH is the most effective efficient cost-sensitive genomic technique to identify
the cytogenetic abnormalities that are essential for risk-stratified therapy in modern
treatment protocols. It is essential to enrich the plasma cells before FISH analysis
to ensure accurate identification of the abnormality.
