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21

NCCN Guidelines for Patients

®

:

Colon Cancer, Version 1.2017

2

Treatment planning

Cancer cell tests

which millions of copies of a DNA part are made.

The copies will be examined for 5 MSI markers.

Tumors can be rated as MSS (

m

icro

s

atellite-

s

table),

MSI-L (

m

icro

s

atellite

i

nstability-

l

ow), and MSI-H

(

m

icro

s

atellite

i

nstability-

h

igh). MSI-H is defined

as the presence of 2 or more MSI markers. MSI-H

suggests dMMR but more testing is needed to

confirm.

An IHC (

i

mmuno

h

isto

c

hemistry) panel is used

to assess MMR proteins. It involves applying a

chemical marker to cells then looking at them with a

microscope. There are four types of MMR proteins.

They are MLH1, MSH2, MSH6, and PMS2. If all are

present, it is unlikely that any

MMR

gene is mutated.

If the MLH1 protein is missing, more testing should

follow. The cancer may be tested for a

BRAF V600E

mutation or a modified

MLH1

gene. If a

BRAF

mutation or modified gene is present, you don’t have

Lynch syndrome. If not present or the other MMR

proteins are missing, the cancer will be tested for

MMR

mutations to confirm Lynch syndrome.

Figure 8

MMR system

A. The four types of MMR

proteins are present to correct

DNA errors when copies of DNA

are being made. An error has

been made in the C-G pair. G has

been replaced by T.

B. The MMR system is deficient.

Some MMR proteins are missing.

A DNA microsatellite has been

shortened in the bottom DNA

copy.

A T C G T C G T A T C T C G T A G

T A G C A G C A T A

T

A G C A T C

A C G T A C

T G C A T G

A T C G T C G T A T C T C G T A G

T A G C A G C A T A G A G C A T C

DNA

factory

MMR

MMR

MMR

MMR

A T C A C A C A C A C A C A T A G

T A G T G T G T G T G T G T A T C

A C G T A C

T G C A T G

A T

C A C A C

T A T C T C G T A G

T A

G T G T G

A T A G A G C A T C

DNA

factory

MMR

Copyright © 2017 National Comprehensive Cancer Network

®

(NCCN

®

).

www.nccn.org

A. Normal MMR

B. dMMR