Decreased expression of 17β-hydroxysteroid dehydrogenase type 1 is associated with DNA hypermethylation in colorectal cancer located in the proximal colon

BMC Cancer

Table 2 The percentage of DNA methylation in CpG rich regions in primary cancerous and histopathologically unchanged tissue samples from patients with CRC.

n = 52		Primary cancerous tissues		Histopathologically unchanged tissues		p^a
		Median (range)	Mean (± SD)	Median (range)	Mean (± SD)
Age
<60	10	21.05 (12.89-25.79)	20.66 ± 4.205	19.47 (13.16-28.42)	19.32 ± 4.875	0.5181
>60	42	20.00 (4.211-33.16)	20.91 ± 7.074	18.95 (2.105-36.21)	18.42 ± 6.779	0.1076
Gender
Female	20	24.21 (16.84-33.16)	24.42 ± 4.516	23.68 (13.68-28.42)	21.75 ± 4.499	0.1155
Male	32	18.95 (4.211-32.11)	19.51 ± 7.255	17.37 (2.105-36.21)	18.43 ± 7.206	0.5594
CRC localization
Proximal colon (cecum to transverse)	20	24.21 ( 13.68-33.16)	23.54 ± 5.793	17.63 ( 2.105435.79)	17.61 ± 6.050	0.0030
Distal colon (splenic flexture to sigmoid)	12	19.47 (4.211-28.95)	19.69 ± 7.159	18.95 (10.53-25.26)	18.85 ± 4.747	0.7498
Rectum	20	19.47 (6.316-28.42)	19.36 ± 6.292	19.47 (4.737-36.21)	19.30 ± 7.851	0.9810
Histologic grade
G1	4	21.32 (13.68-28.42)	21.18 ± 8.067	17.89 (2.105-27.89)	16.45 ± 10.97	0.5126
G2	35	20.00 (10.53-30.53)	21.17 ± 5.293	19.47 (4.737-28.42)	18.93 ± 5.884	0.0996
G3	13	21.84 (4.211-33.16)	20.21 ± 9.397	15.53 (12.63-36.21)	18.11 ± 6.727	0.4021

The primary cancerous and histopathologically unchanged tissue samples from the same patients were used for genomic DNA isolation, followed by bisulfite conversion of cytosine to uracil. The three DNA fragments of the CpG rich region were then amplified by three pairs of primers complementary to the bisulfite-DNA modified sequence (Additional file 1, Additional file 2). To determine the percentage of methylation, the HRM profiles of the patients' DNA PCR products were compared to HRM profiles of the prepared standard PCR products. DNA methylation for each patient was presented as a percentage of methylation in three DNA amplified fragments located in the CpG rich region (Additional file 1). ^a Unpaired, two-tailed t-test.