Lymph node ratio and pN staging in patients with node-positive breast cancer: a report from the Korean breast cancer society.

Patients with node-positive breast cancer are currently classified according to pN stage. Lymph node ratio (LNR), the ratio of positive to total removed lymph nodes, maybe a more useful prognostic factor in these patients. We therefore compared LNR and pN staging as prognostic factors in patients with node-positive breast cancer. Using two large prospective databases of the Korean Breast Cancer Registry (KBCR) and the Asan Medical Center (AMC) Breast Cancer Center of patients with LN-positive breast cancer from 1988 to 2005, we compared the ability of LNR and pN stage to predict patient survival by Cox regression analysis in the overall patient cohort and in subgroups categorized by age and intrinsic subtype. Patients were categorized into low- (≤ 0.20), intermediate- (>0.20 and ≤ 0.65), and high-risk (>0.65) LNR groups. The difference in mortality risk was greater among LNR groups than among patients staged pN1, pN2, and pN3, as assessed by disease-free survival (DFS), cancer-specific survival (CSS), and overall survival (OS) rates. In contrast to LNR risk categories, the survival curves for pN1 and pN2 stage patients overlapped in those aged <35 years and those with her2/neu-enriched or triple-negative tumors. These findings were validated by analyzing a nationwide registry of 15,488 node-positive patients, which showed that patients with pN1 and intermediate LNR risk had poorer DFS (HR 1.7, 95% CI 1.4-2.2) and CSS (HR 1.6, 95% CI 1.1-2.2) than patients with pN2 and low LNR risk. LNR is a better predictor of prognosis than pN stage in women with breast cancer, especially in high-risk patients, including younger women and women with her2/neu-enriched or triple-negative tumors. Treatment decisions should be based on LNR rather than on pN stage.