Molecular Genetics - Colorectal Cancer (IV)

Question 1

4 transmembrane growth receptors targeted in colorectal cancer

Answer 1

EGFR + K-ras status*
HER *
IGF-1R
C-MET

Question 2

2 transmembrane growth receptors in CRC that can predict prognosis

Answer 2

HER - Human epidermal growth factor receptor

EGFR - Epidermal growth factor receptor

Question 3

Activation and downstream effects of HER in CRC

Answer 3

Ligand-induced dimerization > intracellular phosphorylation > MAPK proliferation and PI3K/AKT prosurvival pathways

Question 4

Activation and downstream effects of EGFR in CRC

Answer 4

Receptor tyrosine kinase constitutive activation > tumor growth, proliferation, invasion, metastasis…

Question 5

2 anti-EGFR drugs

Answer 5

Tyrosine kinase inhibitors:

Cetuximab
Panitumumab

Question 6

Which gene is tested to predict CRC response to Tyrosine kinase inhibitor against EGFR?

Answer 6

KRAS status

• Mutated K-ras: no difference between support treatment and cetuximab (TKI)
• Wild Type K-ras: great response to TKI

Mutated KRAS will not benefit from TKI and expose to unnecessary side effects

Question 7

2 routine tests for EGFR status and drug response in CRC

4 special tests for sequencing?

Answer 7

EGFR - IHC for expression at protein level

KRAS - PCR and sequencing of KRAS codon 12 and 13 - predict drug response

qPCR, High resolution melting analysis, restriction enzyme, pyrosequencing

Question 8

4 steps in KRAS sequencing to predict TKI response in EGFR-mutated CRC

Answer 8

1) Micro-dissection
2) DNA extraction
3) PCR amplification
4) Sanger sequencing

Question 9

3 methods to increase sensitivity of KRAS sequencing in EGFR-mutated CRC

Answer 9

1) Identify tumor rich area by pathologist
2) Microdissection of tumor enriched area
3) Minimize size of amplicons

Question 10

Describe the effect of amplicon size on sequencing sensitivity.

Answer 10

longer PCR product = lower chance of successful amplification and subsequent sequencing

Shorter PCR product = high chance of successful amplification and sequencing

Question 11

Rationale behind testing to predict drug response by KRAS status?

Answer 11

KRAS is a major downstream pathway of EGFR signaling

Blockage of EGFR by TKI can cause KRAS constitutive activation and bypass EGFR signaling&raquo_space; TKI resistance