Chronic lymphocytic leukemia (CLL) 

  • Method:
  • Anticoagulant:
  • Recommendation:
  • Method:
    Cytomorphology
  • Anticoagulant:
    EDTA
  • Recommendation:
    obligatory
  • Method:
    Immunophenotyping
  • Anticoagulant:
    EDTA or Heparin
  • Recommendation:
    obligatory
  • Method:
    Chromosome analysis
  • Anticoagulant:
    Heparin
  • Recommendation:
    facultative
  • Method:
    FISH
  • Anticoagulant:
    EDTA or Heparin
  • Recommendation:
    obligatory
  • Method:
    Molecular genetics
  • Anticoagulant:
    EDTA or Heparin
  • Recommendation:
    obligatory

Chronic lymphocytic leukemia (CLL) is the most common leukemic disease in elderly patients. In Germany, the annual incidence in men is 7.4/100.000 and in women 4.8/100.000, and the median age of onset is between 70 and 75 years. The clinical and biological picture of CLL is very heterogeneous. The disease develops from mature B-cells, and is mainly due to the inhibition of apoptosis and dysregulation of proliferation in these cells. In many cases, CLL is preceded by an asymptomatic and unnoticed preliminary stage with proliferation of clonal B cells, which is known as monoclonal B-cell lymphocytosis (MBL).

Classification of CLL

According to the WHO classification 2017, chronic lymphocytic leukemia (CLL), as an indolent lymphocytic lymphoma characterized by a leukemic course, is one of the mature B-cell neoplasms. Differentiation from mantle cell lymphoma, follicular lymphoma or other lymphoma entities must be made by immunophenotyping, cytomorphology, FISH and histology.

CLL WHO classification 2017 (Swerdlow et al., 2017)

Mature B-cell neoplasm:

  • Chronic Lymphocytic Leukemia (CLL)

With

5,600

new cases per year CLL is the most common form of leukemia (Onkopedia guideline CLL: Status 04/2019)

Diagnostische Methoden bei CLL

Prognosis of CLL

IGHV status is an important prognostic marker of CLL

IGHV status is a very important prognostic marker in CLL. The non-mutated status is already associated with a less favourable prognosis in early stage CLL (Damle et al. 1999, Hamblin et al. 1999). 

The presence of a stereotypic B-cell receptor may affect prognosis. Recently, it has been shown that patients with a stereotypic IGHV3-21 rearrangement (subset #2) have a significantly reduced time to treatment regardless of the mutation status (Baliakas et al. 2015, Jeromin et al. 2016). However, there is evidence that the prognosis is modulated by additionally present molecular and cytogenetic changes (Jeromin et al. 2016).

In addition, it was shown that subset #1 and #8 are frequently associated with a very aggressive clinical course in U-CLL, whereas subset #4, which is mostly present in M-CLL, has an indolent course (Stamatopoulos et al. 2017).


FISH abnormalities have prognostic significance in CLL

The abnormalities detected by FISH have prognostic significance. Döhner et al. (2000) developed a hierarchical model, whereby when multiple aberrations occur, the prognosis is determined by the most unfavourable genetic modification (see Table 2). The presence of a 17p deletion or an 11q deletion indicates a less favourable disease course compared to the "normal karyotype" in FISH, whereas the presence of a 13q deletion alone is associated with a more favourable prognosis. Patients with trisomy 12 show a similar prognosis as those with normal karyotype.

Table 2: Prognostic relevance of genetic changes


Genetic aberration

Median survial time in month according to Döhner et al.

Prognosis

17p-deletion

32

adverse

11q-deletion

79

increasingly favourable from top to bottom

+12

114

"normal" (no abnormalities detectable by FISH panel)

111

13q-deletion (sole)

133

favourable

Chromosome band analysis provides further prognostic information

Chromosome band analysis can provide additional prognostic information in addition to the FISH examination. Several studies have shown that a complex aberrant karyotype is an independent prognostic factor that may even exceed the prognostic effect of TP53 alterations (Herling et al. 2016). Recent results show that only a complex karyotype with ≥ 5 aberrations is an independent unfavourable factor. However, a complex aberrant karyotype with 3 or 4 aberrations is only associated with an adverse prognosis if there is an additional TP53 deletion and/or a TP53 mutation. Complex aberrant karyotypes with +12 and +19 show a favourable prognosis (Baliakas et al. 2019).


CLL: TP53 mutations have an adverse prognosis

An adverse effect on overall survival and time to treatment was shown for TP53 alterations. The incidence of TP53 mutations is 8-12% and of TP53 deletions 4-7%, but it is significantly higher in advanced stages and in refractory CLL. TP53 mutations are often associated with 17p/TP53 deletions, but correlate independently with an adverse prognosis (Döhner et al. 2000, Stilgenbauer et al. 2014, Zenz et al. 2010). If one TP53 allele is mutated and the other is deleted, so that no functional TP53 can be formed, this leads to an additive negative effect (Stengel et al. 2016). Biallelic mutations or monoallelic mutations with CN-LOH (copy-neutral loss of heterozygosity) with a dominant negative effect rarely occur (Goh et al. 2011).


The prognostic panel according to Rossi

The prognostic panel according to Rossi et al. 2013 considers both molecular genetic and cytogenetic markers. Patients are divided into four risk groups:

  • High riskTP53 or BIRC3 alterations

  • Intermediary riskNOTCH1 or SF3B1 mutations or 11q deletion

  • Low risk: trisomy 12 or normal karyotype

  • Very low risk: only 13q deletion

This model can be used both for initial diagnosis and during the course of the disease.

Subclones with mutations (especially in the gene TP53) also show the same unfavourable course as patients with corresponding changes in the main clone (Landau et al. 2013, Rossi et al. 2014). Next-generation sequencing enables the detection of these subclonal mutations up to a clinically relevant mutation load of approx. 3%.

In order to be able to better predict the individual course of events, a systematic prognosis index has been developed (International Prognostic Index CLL-IPI, Table 3 and Table 4).

Table 3: International Prognostic Index for CLL

(Variable)

Variable

Risk factor

Points

TP53 status

Deletion and/or mutation

4

IGHV status

unmutated

2

ß2 microglobulin

>3.5 mg/L

2

Stage

Rai I-IV or Binet B-C

1

Age

>65 years

1

Table 4: International Prognostic Index for CLL

(Risik groups)

Risk group

Score

5-year survival rate (%)

low

0-1

93.2

intermediate

2-3

79.3

high

4-6

63.3

very high

7-10

23.3

Calculation of prognosis

Here you can access the calculation of the CLL-IPI score.

Hoechstetter et al. 2020 showed for stage A CLL according to Binet that in addition to age > 60, ß2-microglobulin >3.5 mg/L, an unmutated IGHV status, a del(17p) in FISH, also lymphocyte doubling time <12 months, del(11q), trisomy 12, male sex and NOTCH1 mutations are associated with a shorter survival and a shorter time to first treatment (Hoechstetter et al. 2020). It should be noted that the TP53 mutation status was not evaluated in this study. The final prognostic model includes six independent risk factors weighted relative to the respective hazard ratio. The score can be calculated according to Table 5. Based on the sum of risk points, patients could be stratified into four risk groups, which were of prognostic relevance for the assessment of both overall survival and time to first treatment (TTFT) (Hoechstetter et al. 2020).

Table 5: Prognostic model developed on the basis of patient data from the CLL1 cohort (CLL1-PM)

Independent factor

Status

Punktwerte

del(17p)

detectable

3.5

IGHV status

unmutated

2.5

ß2 microglobulin

>3.5 mg/L

2.5

del(11q)

detectable

2.5

Lymphocyte doubling time

<12 months

1.5

Age at diagnosis

>60 years

1.5

Risk startification by total score
Very low risk: 0-1.5
Low risk: 2-4
High risk: 4.5-6.5
Very high risk: 7-14

A new international prognostic score (IPS-E) was developed for patients with asymptomatic early stage CLL. It provides a prediction of the time to first treatment (TTFT). Three factors with equal weighting (with 1 point each) were determined, which can independently predict TTFT. The factors are: an unmutated IGHV status, lymphocytes > 15x109/L and palpable lymph nodes. This results in 3 risk groups: Low risk (0 points), medium risk (1 point) and high risk (2-3 points). The probability of needing treatment increases from low risk to high risk patients (Table 6 and Table 7). TP53 aberrations play an important role in therapy decisions, but have no prognostic significance in determining the time to treatment (Condoluci et al. 2020).

Table 6: International Prognostic Score 

(IPS-E)

Variable

Risk factor

Points

IGHV status

unmutated

1

Lymphocytes

> 15x109/L

1

Lymph nodes

palpable

1

Table 7: Risk groups 

Risk groups

Score

Cumulative incidence of treatment (5-years,%)

low

0

8.4

intermediate

1

28.4

high

2-3

61.2

Associations between genetic changes and prognosis markers

There are associations between molecular cytogenetic changes (in FISH) and other prognostic markers. For example, CD38-positivity associated with an adverse prognosis (Hamblin et al. 2000, Ibrahim et al. 2001, Jelinek et al. 2001) occurs more frequently together with a higher number of FISH abnormalities and with high risk factors (17p-, 11q-). Furthermore, associations between 11q-deletions and 17p-deletions and an unmuted IGHV status are found (Stilgenbauer et al. 2002; Kröber et al. 2002). Associations of SF3B1 mutations with 11q deletions and NOTCH1 mutations with trisomy 12 have recently been discussed.

In addition, the detection of CD38 expression and cytoplasmic expression of ZAP70 is associated with an adverse prognosis. However, these parameters are of less clinical and therapeutic relevance today.

Baliakas et al. 2019 examined early stage CLL for different prognostic markers depending on the IGHV status. Unfavorable factors in patients with mutated IGHV status are TP53 aberrations, trisomy 12 and the stereotype IGHV3-21 (subset #2). In patients with unmutated IGHV status del(11q), TP53 aberrations and/or SF3B1 mutations and men showed a shorter time to first treatment.

Diagnostic Recommendations of CLL

If a patient is suspected of having CLL, the various guidelines recommend the following tests:

Therapy of CLL

Cytogenetic and molecular changes influence the decision on therapy in CLL

Cytogenetic changes do not only allow an assessment of the prognosis. Rather, increasing data indicate that it is also possible to assess the response to certain therapies on the basis of the cytogenetic changes. This is of great importance, as many new substances have currently found their way into CLL therapy, whose efficacy also varies depending on the presence of certain genetic abnormalities (Hallek 2013, Byrd et al. 2015, O'Brien et al. 2015, Roberts et al. 2016, Onkopedia Guideline CLL: Status 04/2019).

Del(17p13) and TP53 mutations influence choice of first-line therapy

Del(17p13) and TP53 alterations are currently the only prognosis markers that already have a direct influence on the first therapeutic decision. Thus, the presence of TP53 mutations and/or TP53 deletions is prognostically unfavourable and associated with a lower response rate to commonly used standard chemotherapy (Oscier et al. 2013, Stilgenbauer et al. 2014). Since TP53 alterations may be added in the course of the disease, a TP53 analysis should be performed prior to any therapy decision in case of disease progression. Thus, the current Onkopedia guidelines recommend the use of ibrutinib in first-line therapy in patients with CLL requiring therapy and a TP53 alteration, regardless of their general condition (Onkopedia guideline CLL: 04/2019).

Recent studies suggest that patients with a complex aberrant karyotype respond less well to ibrutinib-based treatments (O'Brien et al. 2018, Thompson et al. 2015). However, these patients may benefit from treatment with venetoclax-obinutuzumab (Al-Sawaf et al. 2020)

IGHV mutation status

The IGHV status is an important prognosis marker. It does not change during the course of the disease and should therefore be determined once before a decision on therapy is made. Patients with an unmutated IGHV status have a shorter overall survival and need therapy earlier (Hamblin et al. Blood 1999). The Onkopedia guidelines for CLL recommend therapy with ibrutinib.

There are also mutations in other genes whose effects on the course of the disease and relevance to therapy are currently being investigated. These include the following, each with a frequency of less than 10%: BCOR, EGR2, FBXW7, MYD88, NRAS, POT1, KRAS, SAMHD1, XPO1.

Development of resistance under Ibrutinib therapy

Treatment with ibrutinib may lead to the development of resistance mutations. Known affected genes are the BTK and PLCG2 genes (Woyach et al. 2014). Since mutations in these genes can only be detected after therapy is administered, an examination is only indicated in the case of non-response and not before the start of therapy.

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