Molecular predictors of survival after adjuvant chemotherapy for colon cancer

Abstract

Background: Adjuvant chemotherapy improves survival among patients with stage III colon cancer, but no reliable molecular predictors of outcome have been identified.

Methods: We evaluated loss of chromosomal material (also called loss of heterozygosity or allelic loss) from chromosomes 18q, 17p, and 8p; cellular levels of p53 and p21(WAF1/CIP1) proteins; and microsatellite instability as molecular markers. We analyzed tumor tissue from 460 patients with stage III and high-risk stage II colon cancer who had been treated with various combinations of adjuvant fluorouracil, leucovorin, and levamisole to determine the ability of these markers to predict survival.

Results: Loss of heterozygosity at 18q was present in 155 of 319 cancers (49 percent). High levels of microsatellite instability were found in 62 of 298 tumors (21 percent), and 38 of these 62 tumors (61 percent) had a mutation of the gene for the type II receptor for transforming growth factor beta1 (TGF-beta1). Among patients with microsatellite-stable stage III cancer, five-year overall survival after fluorouracil-based chemotherapy was 74 percent in those whose cancer retained 18q alleles and 50 percent in those with loss of 18q alleles (relative risk of death with loss at 18q, 2.75; 95 percent confidence interval, 1.34 to 5.65; P=0.006). The five-year survival rate among patients whose cancer had high levels of microsatellite instability was 74 percent in the presence of a mutated gene for the type II receptor for TGF-beta1 and 46 percent if the tumor did not have this mutation (relative risk of death, 2.90; 95 percent confidence interval, 1.14 to 7.35; P=0.03).

Conclusions: Retention of 18q alleles in microsatellite-stable cancers and mutation of the gene for the type II receptor for TGF-beta1 in cancers with high levels of microsatellite instability point to a favorable outcome after adjuvant chemotherapy with fluorouracil-based regimens for stage III colon cancer.

Figure 1. Autoradiographs of Molecular Markers

Panel A shows an analysis of allelic deletions on chromosomes 18q (lanes 1, 2, and 3) and 17p (lanes 4, 5, and 6). N denotes non-neoplastic mucosa and T tumor tissue. The carcinomas in lanes 1, 2, 4, and 6 have allelic loss in tumor DNA, as indicated by bands with reduced intensity (arrowheads) as compared with the intensity of matched control DNA from non-neoplastic mucosa. Panel B shows an analysis of microsatellite instability and frame-shift mutations in genes with repeated sequences in coding regions. The tumors in lanes 1, 3, 5, and 6 have allelic shifts (flanked by arrowheads) in dinucleotide markers on chromosomes 18q and 17p, in comparison with the matched control DNA from non-neoplastic mucosa. The carcinoma in lane 7 has shifts (flanked by arrowheads) in the BAT-26 polyadenine tract in the fifth intron of the hMSH2 gene. The tumors in lanes 8 and 9 have mutations (arrowheads) in the polyadenine tract of the gene for the type II receptor for TGF-β1 and in the polydeoxyguanosine tract in the proapoptotic BAX gene, respectively.

Figure 2. Disease-free Survival According to the Analysis of Molecular Markers in Patients with Stage III Colon Cancer Treated with Postoperative Adjuvant Chemotherapy with Fluorouracil-Based Regimens

The rate of disease-free survival was significantly higher in patients whose tumor had no loss of heterozygosity (LOH) at chromosome 18q than in those who did have allelic loss at 18q (Panel A); this was also true in the subgroup of patients with microsatellite-stable tumors (MSS) (Panel B). Patients whose cancers had high levels of microsatellite instability (MSI) had a higher rate of survival than those with microsatellite-stable cancers (Panel C). In the subgroup of those with high levels of MSI, those whose cancer had a mutation in the gene for the type II receptor for TGF-β1 (TGF-β1 RII) had a higher rate of disease-free survival than those without this mutation (Panel D). P values were calculated by the log-rank test.

Figure 3. Overall Survival According to the Analysis of Molecular Markers in Patients with Stage III Colon Cancer Treated with Postoperative Adjuvant Chemotherapy with Fluorouracil-Based Regimens

The rate of overall survival was significantly higher in patients whose cancer had no loss of heterozygosity (LOH) at chromosome 18q (Panel A); this was also true in the subgroup of patients with microsatellite-stable tumors (MSS) (Panel B). The rate of survival in patients whose cancers had high levels of microsatellite instability (MSI) was not significantly different from that in patients with microsatellite-stable tumors (Panel C). Patients with high levels of microsatellite instability and a mutation of the gene for the type II receptor for TGF-β1 (TGF-β1 RII) had a greater rate of survival than those without this mutation (Panel D). P values were calculated by the log-rank test.