Increased frequency of p53 mutation in sporadic colorectal cancer from cigarette smokers

Cigarette smoking has been shown to increase the risk of colorectal cancer. However, the relation between smoking and genetic alterations has not been clarified in this type of cancer.

Mutations of p53, APC, beta-catenin and K-ras-2 genes were analyzed in colorectal carcinomas from 28 smokers and 33 non-smokers. Frequencies and types of mutations were compared between smokers and non-smokers.

The frequency of carcinomas with p53 mutation was higher in smokers (20/28, 71%) than in non-smokers (15/33, 45%) (P = 0.037). The common type of mutation was single-base substitution including G:C to A:T transition in both groups (68% in smokers and 67% in non-smokers). With respect to G:C to A:T transitions, mutation at CpG sites was less frequent in smokers (9/15, 60%) than in non-smokers (10/10, 100%), whereas mutation at non-CpG sites was more frequent in smokers (6/16, 40%) than in non-smokers (0/10, 0%) (P = 0.028). The frequency of APC mutation was not significantly different between smokers (14/28, 50%) and non-smokers (15/33, 45%). No beta-catenin mutation was detected in carcinomas from smokers. K-ras-2 mutation occurred in smokers at a similar frequency (9/28, 32%) to that in non-smokers (13/33, 39%). Concerning pathological aspects, Dukes' A carcinomas were less frequent in smokers (11%) than in non-smokers (33%), whereas Dukes' D carcinomas were more frequent in smokers (25%) than in non-smokers (15%).

The present results suggest that an increased frequency of p53 gene mutation, including G:C to A:T transitions at non-CpG sites, is associated with an increased risk of colorectal carcinogenesis in cigarette smokers.