Association Between Results of a Gene Expression Signature Assay and Recurrence-Free Interval in Patients With Stage II Colon Cancer in Cancer and Leukemia Group B 9581 (Alliance)

Abstract

Purpose: Conventional staging methods are inadequate to identify patients with stage II colon cancer (CC) who are at high risk of recurrence after surgery with curative intent. ColDx is a gene expression, microarray-based assay shown to be independently prognostic for recurrence-free interval (RFI) and overall survival in CC. The objective of this study was to further validate ColDx using formalin-fixed, paraffin-embedded specimens collected as part of the Alliance phase III trial, C9581.

Patients and methods: C9581 evaluated edrecolomab versus observation in patients with stage II CC and reported no survival benefit. Under an initial case-cohort sampling design, a randomly selected subcohort (RS) comprised 514 patients from 901 eligible patients with available tissue. Forty-nine additional patients with recurrence events were included in the analysis. Final analysis comprised 393 patients: 360 RS (58 events) and 33 non-RS events. Risk status was determined for each patient by ColDx. The Self-Prentice method was used to test the association between the resulting ColDx risk score and RFI adjusting for standard prognostic variables.

Results: Fifty-five percent of patients (216 of 393) were classified as high risk. After adjustment for prognostic variables that included mismatch repair (MMR) deficiency, ColDx high-risk patients exhibited significantly worse RFI (multivariable hazard ratio, 2.13; 95% CI, 1.3 to 3.5; P < .01). Age and MMR status were marginally significant. RFI at 5 years for patients classified as high risk was 82% (95% CI, 79% to 85%), compared with 91% (95% CI, 89% to 93%) for patients classified as low risk.

Conclusion: ColDx is associated with RFI in the C9581 subsample in the presence of other prognostic factors, including MMR deficiency. ColDx could be incorporated with the traditional clinical markers of risk to refine patient prognosis.

Fig 1.

(A) REMARK diagram for patients and specimens (initial analysis). (B) REMARK diagram for patients and specimens (final analysis). CALGB, Cancer and Leukemia Group B; RFI, recurrence-free interval; QC, quality control; REMARK, REporting recommendations for tumor MARKer prognostic studies.

Fig 2.

Histogram of continuous ColDx signature score units (n = 393); high risk (≥ 0.4377) in 55% of patients. Data breaks occur between −0.4 and 1.3 at intervals of 0.1. For each interval, the density multiplied by 0.1 estimates the probability of the signature score being in that interval. The distribution mean and standard deviation are 0.46 and 0.24, respectively, with a median of 0.47 and range of −0.33 to 1.26.

Fig 3.

Weighted Kaplan-Meier plot of recurrence-free interval by ColDx signature score dichotomized at the prespecified cut point, 0.4377; 62 and 29 events observed for high and low risk, respectively.

Fig 4.

Weighted Kaplan-Meier plot of overall survival (all deaths regardless of cause) by ColDx signature score dichotomized at the prespecified cut point, 0.4377; 64 and 40 events observed for high and low risk, respectively.