KRAS testing in colorectal
cancer
Philippe Taniere
Birmingham
Targeted therapy in colorectal cancer (CRC)

Two anti EGFR monoclonal antibodies are
licensed for CRC

Cetuximab (Erbitux, Merck Serono)



first line treatment in combination with irinotecan-based
chemotherapy or FOLFOX4
2nd or 3rd line treatment as a single agent
Panitumumab (Vectibix, Amgen)

monotherapy after failure of fluoropyrimidine, oxaliplatin
and irinotecan-containing chemotherapy regimens.
Mandatory molecular testing

KRAS mutation testing is mandatory prior to
prescription since trials have clearly shown
that KRAS mutated tumours will never
respond to the drug

Negative predictive marker
KRAS mutation

KRAS gene mutated in 40 to 45% of CRC


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2 main hotspots in exon 2 at codons 12 and 13
1 rarely mutated site in exon 3 at codon 61
1 even more rarely mutated site at codon 146
Licensing for wild type codons 12 and 13
Sources of material


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Sections from paraffin blocks
Stained sections
Cytology specimens
DNA extraction and PCR
Scraping from slides
Tissue in DNA extraction buffer
Direct sequencing (Sanger)
Substitution
Pyrosequencing

G to T codon 12
GGT
Codon 12
GGC
Codon 13
Real time PCR
View: All Wells
View: Control (3A) and 12 Val mix (3G)
Exogenous Control and
Single Mutation: 12 Val Positive
all 7 K-RAS Mutation Mixes
Exogenous Control. Well 3A
12 Val: Positive. Well 3G
Others, …
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HRM
Snapshot
Etc,..
KRAS and CRC
In practice, tests to be performed within 3 to 5
working days
In practice

Who is paying for testing?



How much does it cost?



NHS
Merck Serono
Very cheap!
When to start on the testing?
Who can do the testing?
Perspective


Only a proportion of patients with wild-type
KRAS respond to anti EGFR monoclonal
antibody
A more advanced assessment of tumour cells
may become justified in the near future


?More codons of KRAS (61 and 146)
?BRAF, PIK3CA, pTEN, etc,..
Need for platforms, kits, etc,..for cheap
and quick multiple screening