Lymph Node Ratio after Neoadjuvant Chemotherapy for Stage II/III Breast Cancer

Restricted mean survival time (RMST), recommended for reporting survival, lacks a tool to analyze multilevel factors. Gini's mean difference of RMSTs, Δ, is proposed and applied to compare a lymph node ratio-based classification (LNRc) versus a number-based classification (ypN) in stage II/III breast cancer patients prospectively enrolled to neoadjuvant chemotherapy who underwent axillary dissection. Number of positive nodes (npos) classified patients into ypN0, npos=0, ypN1, npos=[1,3], ypN2, npos=[4,9], and ypN3, npos≥10. Ratio npos/(number of nodes examined) of 0, (0,0.20], (0.20,0.65], and >0.65, classified patients into Lnr0 to Lnr3, respectively. Unadjusted and Cox-adjusted RMSTs were computed for the ypN and LNRc's. At a follow-up time horizon of 72 months for 114 node-negative and 254 node-positive patients, unadjusted ypN0–ypN3 RMSTs were 62.4–41.4 months, Δ=11.9 months (95%CI: 7.4–16.9), and Lnr0–Lnr3 62.4–36.3 months, Δ=14.0 months (95%CI: 10.1–18.1). Cox models' ypN1–ypN3 hazard ratios were 1.81–3.30, and Lnr1–Lnr3 1.52–4.39. Δ from Cox-fitted survival were ypN 8.1 months (95%CI: 5.9–10.5), LNRc 10.5 months (95%CI: 8.4–12.8). Thus, Gini's mean difference and other model metrics establish lymph node involvement as a foremost predictor of survival. Ratio-classification improved on number-classification for survival prognosis.