No change in lymph node positivity rate despite increased lymph node yield and improved survival in colon cancer

Abstract

Aim

To analyse trends over time in the number of lymph nodes evaluated and in the proportion of node positivity and to investigate the impact on survival for patients with colon cancer.

Patients and methods

8616 patients resected for M0 colon cancer diagnosed in the Southern Netherlands between 2000 and 2011 were included in this study. Trends in nodal evaluation and node positivity were analysed. Multivariable logistic regressions were used to assess the influence of period of diagnosis on adequate nodal evaluation (⩾12 lymph nodes) and node positivity after adjusting for patient and tumour characteristics. Crude 5-year relative survival was used as an estimate for disease-specific survival.

Results

Overall, the proportion adequate nodal evaluation increased from 13% in 2000–2002 to 59% in 2009–2011 (p < 0.0001), whereas the proportion node positivity remained similar across study periods (approximately 35%). Patients diagnosed in later periods were more likely to have received adequate nodal yield (adjusted Odds ratio (OR) 2009–2011 versus 2000–2002 9.8, 95% Confidence interval (CI) 8.3–11.6). However, the adjusted odds of having node positive disease did not differ between periods of diagnosis. Relative excess risk of dying was independently correlated with the number of lymph nodes evaluated (1–8 LNs versus ⩾12 LNs, N0: 2.2, 95% CI 1.7–2.9; N+: 1.7, 95% CI 1.4–2.0) and period of diagnosis (2009–2011 versus 2000–2002, N+ only: 0.8, 95% CI 0.6–1.0).

Conclusion

The reason for improved survival with increased nodal yield is different from simple understaging as the proportion of lymph node positivity remained constant.

Introduction

In the evaluation of quality of care for patients with colon cancer, the number of lymph nodes evaluated has become a surrogate marker for surgical and pathological excellence. Quality initiatives aimed at improving nodal yield have been undertaken in North America and Europe. In the Netherlands, it is measured in different auditing systems and quality registrations.

The focus on nodal yield in colon cancer was fuelled by several non-randomised studies which investigated the relationship between lymph node evaluation and survival. These studies have shown that higher lymph node yield is associated with better survival after colon cancer surgery [1], [2], [3], [4], [5], [6], [7].

Despite the attention for lymph node yield in many studies, the association with nodal positivity rate has not often been articulated. Studies from the US and Canada found that the number of lymph nodes evaluated in colon cancer has increased over the years but the proportion of metastasis containing lymph nodes did not [8], [9]. Two other studies also found no association between the extent of lymph node evaluation and the proportion of lymph node positivity [10], [11].

The aim of this large observational study is to evaluate trends over time in the number of lymph nodes evaluated and in the proportion of positive lymph nodes for patients who underwent resection for stage I–III colon cancer in the Southern Netherlands. More importantly, we investigated whether period of diagnosis is associated with adequate nodal evaluation and node positivity rate after adjusting for patient and tumour characteristics. Furthermore, the impact on relative survival was investigated.