Lecture 22 - Leukaemia and its treatment

What is Acute Lymphoblastic Leukaemia?

• Clonal expansion of lymphoid progenitors 

  • B-cell, pre-B cell and T-cell 

  • Most commonly the cause of death is from malignancy  

What are the symptoms of ALL?

• Generalised weakness and fatigue  

• Anaemia 

• Excessive bruising/bleeding 

• Unexplained/Rare infections and fever  

• Enlarged lymph nodes 

What chromosomal abnormalities are seen in ALL?

• Numerical 

  • Hyperdiploidy 

  • Hypodiploidy 

• Structural

  • Chromosomal translocations

    • T(12;21)

    • T(9;22)

    • Translocations involving mixed lymphoid leukaemia (MLL) gene

What is Hyperdiploidy?

• More chromosomes

What is hypodiploidy?

• Less chromosomes

How often is T(12;21) seen in ALL?

• 25% of cases

How often is T(9;22) seen in ALL?

• 3% of cases

Which age group are translocations involving mixed lymphoid leukaemia (MLL) gene seen?

• Mostly seen in infants 

Why do chromosomal translocations result in ALL development?

• Leads to fusion proteins 

  • Gene fusion results in chimeric A-B fusion genes being translated into fusion proteins 

  • These fusion proteins are related to normal gene function 

    • E.g. ABL in BCR/ABL 

What is Core binding factor protein A-2?

• Core binding factor protein A-2 (CBFA-2)(RUNX1) is a heterodimeric transcription factor made of RUNX1 and CBFB

  • Plays a role in regulating blood cell development 

  • Either activates or represses its target genes by recruiting p300 or HDAC respectively 

CBFA-2/RUNX1 activates its target genes by recruiting…

• p300

CBFA-2/RUNX1 represses its target genes by recruiting…

• HDAC

What is EVT6 RUNX1 protein?

• Fusion gene which recruits HDAC complex 

• Allows formation of a very stable repressor complex 

  • Represses RUNX1 target genes

How does the MLL gene play a role in ALL?

• Encodes a DNA binding protein which methylates histones 

  • Positively regulates gene expression, including HOX genes 

• However, fusion genes of MLL lose intrinsic methyltransferase activity but gain the ability to form complexes to bind targets as well as recruiting the methyltransferase DOT1L

  • This represses differentiation of lymphocytes while overexpressing HOX genes driving proliferation

What is the methyltransferase which fusion MLL proteins can recruit to hypermethylate histones?

• The methyltransferase DOT1L

How is sex a prognostic factor of ALL at diagnosis?

• Males generally perform worse 

How is age a prognostic factor of ALL at diagnosis?

• >10 years old have worse prognosis

How is while blood cell count a prognostic factor of ALL at diagnosis?

• High white blood cell count generally indicates a poor prognosis

How is where the cancer spreads a prognostic factor of ALL at diagnosis?

• Cancer spread to brain/spinal cord 

  • Associated with worse prognosis 

In ALL patients, Philadelphia chromosome and hypodiploidy are associated with _____ prognosis.

In ALL patients, Philadelphia chromosome and hypodiploidy are associated with worse prognosis.

In ALL patients, T(12;21) and Hyperdiploidy are associated with _____ prognosis.

In ALL patients, T(12;21) and Hyperdiploidy are associated with better prognosis.

>25% leukaemic blasts at day 8-15 of treatment is associated with______?

>25% leukemic blasts at day 8-15 is associated with a higher risk of relapse.

What is minimal residual disease?

• Refers to the small number of cancer cells that remain in a patient's body during or after treatment

  • Often a good indicator of relapse risk

How does minimal residual disease relate to patient prognosis?

• Presence of minimal residual disease is closely related to the risk of relapse 

  • Risk of relapse rises steeply with the amount of minimal residual disease 

  • Also independent of other prognostic factors 

What is somatic rearrangement which occurs during lymphocyte development?

• T-cell receptor and immunoglobulin loci undergo somatic rearrangement to allow the recognition of millions of diverse antigens 

  • Receptors have heavy and light chains with both constant and variable regions

  • These regions are rearranged to produce unique receptors

How can somatic rearrangements be used in minimal residual disease assessments?

• Identify specific clonal rearrangement of the child’s leukaemic cells 

• Use PCR to specifically detect any residual leukemic clone 

  • Sensitivity -0.01 to 0.001% 

What is Taqman Hydrolysis Probes?

• Probe is conjugated with a quencher fluorochrome which absorbs the fluorescence of the reporter 

• On amplification of the target, the 5’ exonuclease activity of Taq polymerase hydrolyses the probe causing separation of reporter and quencher 

• This generates a fluorescent signal 

• Each consecutive cycle causes exponential reporter fluorescence 

  • This can then be measured using a computer  

What are the therapeutic approaches to treating ALL?

• Chemotherapy 

  • Combination of many different therapies 

• Radiation therapy 

  • Painful in bony areas and high disease burden 

  • Bone marrow transplant

    • Requires whole body radiation

• Intensive combined chemo and radio therapy 

• Surgery 

• Novel agents  

Early during ALL treatment, what was the treatment given?

• Early on therapy was not given

  • As drugs started to be given, more children were surviving

What are the key clinical challenges of treating ALL in children?

• Toxicity issues 

• Overtreatment of some cancers 

How can treatment be tailored to each patient?

• Use of prognostic markers to tailor treatment 

  • Poor prognostic patient groups receive more intensive therapy to improve chances of survival 

  • Good prognostic patient groups may be considered for less intensive protocols 

    • Reduce toxicity without reducing survival rates 

The study which attempted tailored treatment based on prognostic markers found what?

• Treatment reduction was possible  

  • Patients on intermediate treatment who responded well could be given less treatment with no difference in survival or relapse  

• Treatment intensification also aided patients

  • Showed increasing treatment appeared to help patients who responded poorly to initial treatment

  • HOWEVER, overall survival was not significant due to the increased toxicity  

Imatinib is a targeted therapy which targets what? What type of cancer can it be used to treat?

• Targets the BCR-ABL fusion protein and competitively inhibits it

  • Can therefore only be used on Philadelphia chromosome-positive CML/ALL as the BCR-ABL fusion protein is present

Continuous imatinib exposure in Ph+ ALL patients resulted in what?

• Continuous imatanib exposure improved outcome 80% event free survival when compared to historical controls (35%) 

  • There were no significant toxicities associated with adding imatinib to intensive chemotherapy  

What are the current critical challenges in ALL treatment?

• Further increase survival rates

• Achieve a cure with minimal toxicity