One hundred and twenty-seven monochronous primary colorectal adenocarcinomas were examined for both activation of the c-Ki-ras proto-oncogene by point mutation in codons 12 or 13 and inactivation of the p53 tumour suppressor gene by point mutation in exons four through nine. All of the carcinomas originated in the distal half of the colorectum. Activation of the c-Ki-ras proto-oncogene was detected in 23% (29/127) of adenocarcinomas, and p53 inactivation was detected in 63% (80/127) of adenocarcinomas. Only 16% (20/127) of cases exhibited both genetic changes, and no association was noted between the occurrence of these two changes. Individually, both ras activation and p53 inactivation were associated with a poorer patient prognosis (p=0.0009 and p=0.0159 respectively). In a Cox regression analysis both ras activation and p53 inactivation contributed independently towards patient mortality. These results suggest that mutations exert their effect independently of each other, and that it is the cumulative mutational load that determines a patient's prognosis.

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