K-ras mutation in colorectal cancer: relations to patient age, sex and tumour location.

DNA from 251 primary tumours obtained from 123 male and 125 female Norwegian patients with colorectal carcinoma was analysed for the presence of K-ras point mutations at codons 12 and 13. Mutations were found in 99 (39%) of the samples. The frequency of K-ras mutations was significantly related to age and sex of the patients, and to the location of the tumours (overall: P = 0.008). K-ras mutations were much less frequent in colonic tumours from male than female patients at younger ages (< 40 years, odds ratio < 0.014). The low frequency might indicate that a different, ras-independent, pathway to neoplasia is dominating in the colon of younger males. In contrast, older men had more mutations than older women (e.g. 90 years, odds ratio = 5.8). An inverse but less pronounced relationship was seen for rectal tumours. The type of mutation was found to be associated to sex of patient and location of tumour. G-->C transversions accounted for 35% of the mutations in rectal tumours from females, in contrast to only 2.5% in the rest of the material (P = 0.0005). This may indicate that there are specific carcinogens acting in this location.