Table 1

Frequency of alkylation (number (%)) and O6-methylguanine concentrations (mean (SD)) in DNA isolated from macroscopically normal and malignant tissue samples from the colon and rectum

Normal tissueTumour tissue
(No positive/
total No (%))
Concentration1-a (μmol O6-MedG/ mol dG)Frequency
(No positive/
total No (%))
Concentrationa(μmol O6-MedG/ mol dG)
Proximal colon1-b  4/16 (25)0.021 (0.003)1 2 3  9/15 (60)0.044 (0.030)
Sigmoid colon11/21 (52)0.044 (0.025)c 1 3  6/19 (32)0.050 (0.050)
Rectum12/25 (48)0.042 (0.020)2 15/24 (63)0.046 (0.048)
  • 1-a Levels inO 6-MedG containing samples.

  • 1-b Tumours of the caecum, hepatic flexure, and transverse colon.

  • 1-c Levels are 0.126 (0.27) μmolO 6-MedG/mol dG if positive outlier is included.

  • Alkylation levels in normal DNA from the proximal colon were lower than those in normal DNA from the sigmoid colon (1p=0.04, Mann-Whitney U test) or rectum (2p=0.03 Mann-Whitney U test). Inclusion of the positive outlier result did not alter the results (3p=0.05, Mann-Whitney U test).