Quantitative lymph node evaluation as an independent marker of long-term prognosis in stage III rectal cancer.

Background:  The prognostic significance of lymph node evaluation is not well described for rectal cancer due to a lack of reproducibility in nodal counts and variable use of adjuvant and neoadjuvant therapy. The aim of this study was to examine the role of quantitative lymph node evaluation as an independent marker of prognosis in stage III rectal cancer. Methods:  New Zealand Cancer Registry data were retrieved for consecutive patients with rectal cancer from January 1995 to July 2003. Cases with node-negative tumours, distant metastases, death within 30 days of surgery and incomplete data fields were excluded. Three nodal stratification systems were investigated – Total Number of Nodes examined (TNN), Absolute number of Positive Nodes (APN) and Lymph Node Ratio (LNR). Univariate and Cox regression analyses were performed with 5-year all-cause mortality as the primary end point. Results:  The study identified 895 stage III rectal cancer cases. The mean APN and LNR were significantly higher in patients who died within 5 years. An increasing APN or LNR was associated with a significant increase in 5-year mortality. The APN and LNR were also powerful predictors of 5-year mortality after correcting for other factors using Cox regression. The TNN was of no prognostic significance. Conclusions:  Both the APN and LNR are highly effective at independently predicting and stratifying 5-year mortality in stage III rectal cancer. The significant predictive value of the LNR is likely to be a reflection of the APN rather than one functioning in autonomy, given that the TNN was of no prognostic significance.