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20

NCCN Guidelines for Patients

®

:

Acute Lymphoblastic Leukemia, Version 1.2017

2

Testing for ALL

Genetic tests

Many types of chromosome changes can happen

in ALL. The leukemia cells may have an abnormal

number of chromosomes—too many or too few. The

leukemia cells may also have more than one type of

chromosome change.

Sometimes parts of chromosomes break off and

switch with each other. This is called a translocation.

The Philadelphia chromosome is a key example of

a translocation that happens in some people with

ALL. The Philadelphia chromosome is caused by a

translocation between parts of chromosomes 9 and

22.

See Figure 6.

This translocation also forms the abnormal

BCR-ABL

fusion gene on the Philadelphia

chromosome. A fusion gene is a new gene that is

formed when parts of two separate genes are joined

(fused) together.

FISH

FISH (

f

luorescence

i

n

s

itu

h

ybridization) is a very

sensitive lab test that can detect certain abnormal

changes in a cell’s genes or chromosomes. It can

detect most abnormal changes that can be seen

with a microscope. It can also detect some changes

that are too small to be seen with basic cytogenetic

testing (karyotyping).

Figure 6

Philadelphia

chromosome

The Philadelphia

chromosome is formed by a

translocation between parts

of chromosomes 9 and 22.

It contains the abnormal

BCR-ABL

fusion gene.

This is a key chromosome

change that affects which

treatments are best for you.

Chromosome 9

ABL

gene

Chromosome 22

BCR

gene

BCR-ABL

gene

Philadelphia

chromosome

Chromosome 9

Normal chromosomes

Chromosomes break Changed chromosomes

Chromosome 22

BCR

gene

Chromosome 9

ABL

gene

Illustration Copyright © 2017 National Comprehensive Cancer Network

®

(NCCN

®

)