Evaluation of guanylyl cyclase C lymph node status for colon cancer staging and prognosis

Purpose: The prognostic significance of guanylyl cyclase C (GCC) gene expression in lymph nodes (LNs) was evaluated in patients with stage II colon cancer who were not treated with adjuvant chemotherapy. We report a planned analysis performed on 241 patients. Methods: GCC mRNA was quantified by RT-qPCR using formalin-fixed LN tissues from patients with untreated stage II colon cancer who were diagnosed from 1999-2006 with at least ten LNs examined and blinded to clinical outcomes. Lymph node ratio (LNR) is the number of GCC-positive nodes divided by total number of informative LNs. Risk categories of low (0-0.1) and high (> 0.1) for LNR were chosen by significance using Cox regression models. The data were tested for association with time to recurrence. Results: Twenty-nine patients (12%) had a disease recurrence or cancer death. The LNR significantly predicted higher recurrence risk for 84 patients (34.9%) classified as high risk (hazard ratio (HR), 2.38; P = 0.02). The estimated 5-year recurrence rates were 10% and 27% for the low-and high-risk groups, respectively. After adjusting for age, T stage, number of nodes assessed, and MMR status, a significant association remained (HR, 2.61; P = 0.02). In a subset of patients (n = 181) with T3 tumor, ≥ 12 nodes examined and negative margins, a significant association between the GCC LNR and recurrence risk also was observed (HR, 5.06; P = 0.003). Conclusions: Our preliminary results suggest that detection of GCC mRNA in LNs is associated with risk of disease recurrence in patients with untreated stage II colon cancer. A larger validation study is ongoing.