Frequent mutations of the CA simple sequence repeat in intron 1 of EGFR in mismatch repair-deficient colorectal cancers

Table 3 Relationship between EGFR CA-SSR I genotypes and EGFR expression levels in colorectal tumors

	CA-SSR genotypes1		CA-SSR I status2 of the tumor	EGFR expression
	Normal colon	Tumor		QRT-PCR3	IHC4
1	16/16	16/20	MSI	0.87	++ m
2	16/16	16/16	MSS	0.70	++ m
3	16/18	16/18	MSS	2.68	++ m
4	16/16	14/16/20/(21/22/23)	MSI	5.10	+++ m, c
5	20/20	16/25/26/27	MSI	0.27	++ m, c
6	20/20	20/20	MSS	0.76	++ m
7	16/20	16/20	MSS (AI +)	1.11	+++ m
8	20/20	20/20	MSS	0.48	++ m
9	16/20	16/20	MSS	3.68	++ m
10	16/16	16/16	MSS	1.32	++ m
11	16/18	16/18	MSS (AI +)	0.47	+ m
12	19/21	19/21/(22/23)	MSI	1,57	+++ m, c
13	16/18	14/16/18	MSI	ND	++ m, c
14	14/20	12/14/20/(22/23)	MSI	ND	++ m, c
15	16/18	16/18/(23/24)	MSI	ND	+++ m, c
16	16/20	16/20	MSS	ND	-
17	16/16	16/16	MSS	ND	-
18	18/18	18/18	MSS	ND	++ m

¹CA-SSR I alleles determined in colorectal tumors and corresponding normal tissues (germline alleles). All observed alleles are indicated, with minor alleles in brackets;

²MSI, presence of CA-SSR I instability; MSS, absence of CA-SSR I instability; AI +, presence of allelic imbalance;

³Relative expression of EGFR mRNA levels (tumor relative to matching normal tissues), as assessed by QRT-PCR and calculated using the 2^-ΔΔCt formula. Values corresponding to a fold change > 2 or < 0.5 are indicated in bold. ND: not determined;

⁴Expression of EGFR peptide determined by immunohistochemistry. Score 0, 0% of positive cells with membranous staining; 1+, > 0%-1%; 2+, 2%-50%; 3+, > 50%. m: Membranous staining; c: Cytoplasmic staining.