Presence of 18q loss of heterozygosity (LOH) and disease-free and overall survival in stage II colon cancer: CALGB Protocol 9581

Abstract

4012 Background: LOH at 18q is associated with poorer overall survival in patients with colon cancer; however available studies are retrospective and vary in analysis methods. We recently completed an 18qLOH assay method validation study, and after standardizing technique, this prospective study investigated the role of 18qLOH among patients with low-risk stage II colon cancer. Methods: In Cancer and Leukemia Group B (CALGB) protocol 9581, we randomized 1738 stage II patients to post-operative treatment with a 500 mg loading dose of monoclonal antibody 17–1A followed by four infusions of 100 mg every 28 days or observation. The primary endpoint was overall survival (OS); disease free survival (DFS) was a secondary endpoint. Status of 18qLOH was assessed in patients with available tissue and interpretable PCR results. Patients were excluded if their tumors were uninformative for 18qLOH or if their tumors displayed microsatellite instability. Results: We report 18qLOH data on 156 patients. Patient characteristics including treatment, age, gender, performance status, site and grade of tumor, were similar between all patients enrolled and the subset of patients with tumor samples analyzed. The DFS and OS for treated and observed patients were no different (5-yr DFS: 0.81 and 0.80, p= 0.96; 5-yr OS: 0.88 and 0.86, p=0.44 at a median of 6.8 yrs of follow-up) and the data were pooled across the study's arms. Of the tumors examined, 101 (65%) were positive for 18qLOH. A significantly lower proportion of patients with 18qLOH-positive tumors had proximal tumors (46.5% vs 65.5%; p=0.02). Significantly decreased DFS and OS were observed in patients with 18qLOH-positive tumors. Five-year DFS among patients with 18qLOH-positive tumors was 0.78 vs 0.93 among patients with 18qLOH-negative tumors [HR 0.39; 95% CI (0.16, 0.94); logrank p=0.03 based on 33 events]. Five-year OS among patients with 18qLOH-positive tumors was 0.85 vs 0.98 among patients with 18qLOH-negative tumors [HR 0.25; 95% CI (0.07, 0.83); logrank p=0.01 based on 24 events]. Conclusions LOH at 18q was prognostic for DFS and OS among patients with available tissue for analysis after resection of low-risk stage II colon cancer who were not treated with chemotherapy in the adjuvant setting. [Table: see text]