Cytogentic Services in Leukaemia - ALL Flashcards
Outline the risk groups that came out of the ALL97 childhood trial.
GOOD:
- high hyperdiploidy (51-65 chromosomes)
- t(12;21) = ETV6-RUNX1 translocation
INTERMEDIATE:
- t(1;19)(q23;p13), IGH-CEBP, IGH-ID4, del(6q), abn(9p)
- abn(11q), dup(1q), -7, dic(9;20), dic(9;12)
- any other abnormalities, normal karyotype
POOR:
- t(9;22), iAMP(21), MLL tranlocations
- Near haploidy (<30 chromosomes), low hypohaploidy (30-39 chromosomes), t(17;19), abnormal 17p, loss of 13q.
What cytogenetic changes are classified as good prognosis for ALL (according to ALL97)?
GOOD:
- high hyperdiploidy (51-65 chromosomes)
- t(12;21) = ETV6-RUNX1 translocation
What cytogenetic changes are classified as intermediate prognosis for ALL (according to ALL97)?
INTERMEDIATE:
- t(1;19)(q23;p13), IGH-CEBP, IGH-ID4, del(6q), abn(9p)
- abn(11q), dup(1q), -7, dic(9;20), dic(9;12)
- any other abnormalities, normal karyotype
What cytogenetic changes are classified as poor prognosis for ALL (according to ALL97)?
POOR:
- t(9;22), iAMP(21), MLL tranlocations
- Near haploidy (<30 chromosomes), low hypohaploidy (30-39 chromosomes), t(17;19), abnormal 17p, loss of 13q.
What have been reported as the high risk cytogenetic categories for ALL in the latest childhood ALL trial (UKALL2011)?
POOR PROGNOSIS (CHILD):
- iAMP21
- t(17;19)
- MLL rearrangement
- Near haploidy
- Low triploidy
Try to find these as a high risk finding will alter the path that treatment will take.
What have been reported as the high risk cytogenetic categories for ALL in the latest adultt ALL trial (UKALL14)?
POOR PROGNOSIS (ADULT):
- Philadelphia chromosome / t(9;22)(q34;q11) / BCR-ABL1
- t(4;11)(q21;23) / MLL-AF4
- Low hypohaploidy (30-39 chromosomes) / near-triploidy (60-78 chromosomes)
- Complex karyotype
Outline a general strategy for diagnostic samples in childhood ALL.
1) . G-banded analysis.
2) . FISH for specific abnormalities - t(12;21) = ETV6-RUNX1, BCR-ABL1, MLL, TCF3 to detect t(17;19).
What is the most common translocation you see in ALL?
t(12;21) for ETV6-RUNX1 is the most common translocation that you will find in ALL. Found in about 25% of childhood ALL.
How do we test for the t(12;21) ETV6-RUNX1 translocation in ALL?
- The balanced translocation t(12;21) is cryptic on G-banding since the size and banding pattern of the translocated sections look the same.
- Paediatric trial for ALL97 required all samples to be FISHed using a probe to detect t(12;21)(p13;q22) as this was found in approximately 25% of cases.
- Use FISH to detect the translocation. The probes used covers the ETV6 gene (formerly known as TEL) on chromosome 12p (green) and the RUNX1 gene on chromosome 21 (orange)(formerly known as AML1).
- When a balanced translocation is present of t(12;21) you would expect to see the green probe associated with 12p moved over to 21q and you expect half of the red probe to be moved over to the 12.
- Using these probes in a normal interphase you would expect to see 2R and 2G corresponding to two normal copies of ETV6 on 12p (green) and two normal copies of RUNX1 on 21q (red).
- In a positive interphase you would see 2R, 1G, and 1F.
One normal copy of RUNX on 21q (=1R).
One normal copy of ETV6 on 12p (=1G).
The second copy of RUNX probe has been separated into two parts. One part is translocated onto the derivative 12 (=1R), and the other is in the fusion ETV6-RUNX1 on der21 (=1F).
- If positive get a new fusion formed ETV6-RINX1 so the red and green signals are fused.
How can high hyperdiploidy be detected using ETV6-RUNX1 probe.
- HighHhyperdiploidy (HeH) has 51-65 chromosomes instead of 46, usually includes additional copies of chromosomes 21 and therefore when the probe for t(12;21) is used you get the additional signals from the extra chromosome 21.
- In HeH with the ETV6-RUNX1 probe we are going to see 4 reds and 2 greens - 2 normal copies of ETV6 on 12p and 4 normal copies of RUNX1 on 21q and confirms the +21, +21 part of the karyotype.
What ALL abnormalities can be detected on FISH using the ETV6-RUNX1 probe set?
- ETV6-RUNX1 balanced translocation.
- High Hyperdiploidy (HeH).
- iAMP21.
How can we detect the ALL iAMP abnormality?
- ETV6-RUNX1 probe can again be used.
- iAMP21 = intrachromosomal amplification on chromosome 21.
- They consistently show 5 or more signals of RUNX1 by FISH corresponding to 3 or more extra copies of the RUNX1 gene on a single abnormal chromosome 21.
- Clusters of red signals corresponding to iAMP21 chromosome, 1 red corresponding to a normal copy of chromosome 21 and 2 green signals corresponding to two normal copies of chromosome 12.
What chromosome can RUNX1 be found on?
Chromosome 21q.
What chromosome can ETV6 be found on?
Chromosome 12p.
What is the prognosis of iAMP21 in ALL?
- Poor prognosis shown in ALL97 - however, the data from following trial ALL2003 showed some improvement in outcome for iAMP21 compared to ALL97 because those patients went on to the high risk treatment arm - i.e. outcome is not as poor given the right treatment.
