Changes in the Ki‐67 labeling index between primary breast cancer and metachronous metastatic axillary lymph node: A retrospective observational study

BACKGROUND: The Ki‐67 labeling index (LI) is a well‐known prognostic factor for primary breast cancer, but its clinical significance for metachronous axillary lymph node (ALN) recurrence has not been well documented. METHODS: Ki‐67 expression in primary tumors (PTs) and ALN metastases (ALNMs) was evaluated in 21 patients and quantified to investigate the relationship between Ki‐67 LIs in PTs and metachronous ALNMs. RESULTS: The median Ki‐67 LIs in the PTs and ALNMs were 25.2% (range: 2.3–80.2%) and 70% (range: 10.4–97.4%), respectively. A majority of patients had higher Ki‐67 LIs in ALNMs than in PTs (76.2%, 16/21). Disease‐specific survival was significantly better in patients with a lower‐than‐median ALNM Ki‐67 LI (P = 0.019, log‐rank test). Receiver operating characteristic curves showed a PT Ki‐67 LI of 62.8% as the optimal cutoff value and an ALNM Ki‐67 LI of 65.1%. Accordingly, we divided the patients into four groups: PT Ki‐67 LI lower than 62.8%/ALNM Ki‐67 LI lower than 65.1%, PT Ki‐67 LI lower/ALNM Ki‐67 LI higher, PT Ki‐67 LI higher/ALNM Ki‐67 LI higher, and PT Ki‐67 LI higher/ALNM Ki‐67 LI lower. Disease‐specific survival was significantly better in patients with Ki‐67 LI lower/ALNM Ki‐67 LI lower than in the other groups. CONCLUSION: This is the first study to show that the Ki‐67 LI in metachronous ALNM is a prognostic factor for patients with metachronous ALN recurrence of breast cancer.