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20

NCCN Guidelines for Patients

®

:

Colon Cancer, Version 1.2017

Cancer cell tests

Tissue removed from your body will be sent to a

pathologist. This may be tissue from a biopsy or

surgery. The pathologist will examine the samples

using a microscope.

Pathology report

The pathologist will study the parts of the cells to

classify any disease. This is called histologic typing.

When cancer is found, he or she will do other tests to

learn more about the cancer.

One important test result is the cancer grade. The

cancer grade is a score assigned by the pathologist.

He or she will rate the cancer based on how the

cancer cells look. The score is a sign of how fast the

cancer will likely grow and spread. Higher scores

mean that the cancer will likely grow and spread fast.

All lab results are recorded in a pathology report.

A report will be written each time tissue is removed

from your body and tested for cancer. These reports

are vital to planning treatment.

Review your pathology report(s) with your doctor. Ask

questions if you don’t understand. This information

can be complex. It’s also a good idea to get a copy of

your pathology report(s) and take notes.

Molecular testing

Not all colon cancer cells are alike. Cancer cells can

differ by which genes have mutations. Some gene

mutations are known to have an effect on cancer

treatment. Molecular testing includes tests of genes

or their products (proteins). Molecular testing that is

advised for colon cancer is described next.

RAS mutation

RAS is a family of proteins found in cells. Some

colon cancers have abnormal genes that control

the RAS proteins. As a result, the RAS proteins are

overactive and promote cancer cell growth. Some

treatments for metastatic colon cancer do not work

if the

RAS

genes are abnormal. Thus, testing for

mutations in

KRAS

and

NRAS

genes is advised for

metastatic disease.

BRAF mutation

The BRAF V600E mutation is also known to affect

some treatments. About 5 to 9 out of every 100 colon

cancers have a mutated

BRAF

gene. Testing for

the

BRAF V600E

mutation is advised for metastatic

disease.

MMR and MSI

Normal MMR (

m

is

m

atch

r

epair) proteins correct

DNA errors that occur when copies of DNA are

being made. In some colon cancers, MMR mutations

cause one or more MMR proteins to be absent. As a

result, DNA errors aren’t corrected and the number

of gene mutations increases. Doctors call this dMMR

(

d

efective

m

is

m

atch

r

epair).

The DNA errors caused by dMMR often occur in

microsatellites. Microsatellites are a tiny part of the

DNA code that is repeated many times in a row.

See Figure 8.

Due to dMMR, microsatellites may

be shorter or longer than normal. This is called MSI

(

m

icro

s

atellite

i

nstability).

Loss of MMR proteins and MSI are features of Lynch

syndrome. One or both features is present in over

90 of every 100 Lynch syndrome-related cancers

(>90%). However, these features can still occur in the

absence of Lynch syndrome. They are found in about

15 out of every 100 colon cancers (15%) without

Lynch syndrome.

Testing for loss of MMR proteins or MSI is advised

for all people with colon or rectal cancer. These

features may affect your treatment plan. There are

two tests that can be done.

PCR (

p

olymerase

c

hain

r

eaction) is a test that can

assess for MSI. The test consists of a process in

2

Treatment planning

Cancer cell tests