KRAS Mutations Are Not Predictive for Progression of Preneoplastic Gastric Lesions¹

Sequential steps of precancerous changes often precede intestinal-type gastric carcinoma. These steps include atrophic gastritis, IM³ (type I, complete,or small intestinal metaplasia; and type III, incomplete, or colonic intestinal metaplasia), and dysplasia (reviewed in Ref. 1). Mutations in KRAS are detected in many types of human tumors and have been associated with development and progression (2). Recently, we analyzed the KRASmutation status of premalignant stomach biopsies taken at baseline and at 36 months from 160 individuals from Colombia who had a high risk for developing gastric cancer and were enrolled in a 2³ factorial intervention trial. In that study, we found that those with baseline KRAS mutations were 3.76 times more likely to progress from either atrophy to metaplasia or from complete metaplasia (type I) to incomplete metaplasia (type III; P = 0.05; Ref. 3). When the odds ratio was adjusted for intervention therapy, the estimate was unchanged and statistically significant (odds ratio, 3.74; P =0.04). The presence of baseline KRAS mutations was a significant predictor of progression at 36 months.

In the present study, biopsies were taken from 142 of the 160 study subjects who returned for 72-month follow-ups. They were analyzed for KRAS mutation and for progression/regression of stomach lesions. The hypothesis: baseline KRAS mutations predict histological progression of premalignant stomach lesions.

Eight hundred and sixty-three individuals with chronic multifocal atrophic gastritis were recruited from the towns of Pasto and Tuquerres of Nariño in the southern Colombian Andes. In this region, the incidence of gastric cancer ranks as one of the highest in the world(150/100,000; Ref. 4). The estimated Helicobacter pylori prevalence is >90% among asymptomatic adults (5). The volunteers were agricultural or blue-collar workers of Spanish-Indian (“mestizo”) extraction. The demographic characteristics of the volunteer population have been described previously (6). Endoscopic evaluations of individuals from the community who volunteered to participate in the study were performed in the Hospital Departmental (Pasto, Colombia) after obtaining informed consent approved by the local Human Subjects Committee and the Louisiana State University Health Sciences Center Institutional Review Board. Infection with H. pylori was detected by the Steiner modification of the Warthin-Starry staining method using baseline biopsies.

Volunteer individuals were randomized into treatment groups using a 2³ factorial design as described previously (3). A systematic sample of 160 participants was selected from each of the eight treatment combinations for this study. Of these 160 individuals, samples were available from 142 at 72 months. The anti-Helicobacter treatment consisted of a 2-week course of amoxicillin (500 mg, three times per day), metronidazole (400 mg, three times per day), and bismuth subsalicylate (262 mg, four times per day). Ascorbic acid (1-g tablet, twice per day) and/or β-carotene (30-mg capsule, once per day) or matched placebos for these two drugs(provided by Hoffman-La Roche, Inc.) were given throughout the study. Compliance was assessed by quarterly pill-counts as well as by measurement of serum antioxidant levels at the time of the third endoscopy. Compliance was consistently >90%, as measured by pill-count. Biopsies from 160 individuals (20 from each group) were used to detect KRAS mutations in a double-blinded study at 36 months (3). Biopsies, DNA isolation, mutation detection by denaturing gradient gel electrophoresis, DNA sequencing, and statistical analyses have all been described previously in detail (3).

Of the 160 original volunteers, histological diagnoses were available for 142 individuals after 72 months of follow-up. As seen in Table 1, 12 of 142 (8.4%) progressed to a higher histological stage, 81 of 142(57.0%) did not change, and 49 of 142 (34.5%) regressed. There was no association between histological change at the end of 6 years of follow-up and KRAS mutation status at baseline(P = 0.934). This was somewhat surprising, given our previous finding that baseline KRAS mutations strongly predicted histological progression after 36 months of follow-up (3).

Of the 142 individuals for whom histological diagnoses were available, KRAS mutation status was determined in 136 after 72 months of follow-up. Again, as seen in Table 1, there was no association between KRAS mutation status at 72 months and histological progression or regression.

Given our encouraging preliminary study that indicated that the presence of detectable KRAS mutations at baseline was a strong predictor of future progression (3), it is disappointing that after longer follow-up the association did not hold. Given the worldwide frequency of gastric cancer and the poor 5-year survival rate associated with this disease, a reliable prognostic indicator for the development of stomach cancer is badly needed.