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.