Ki67 increase after core needle biopsy associated with worse disease outcome in HER2-negative breast cancer patients

Ki67 would change after core needle biopsy (CNB) in invasive breast cancer. However, whether Ki67 alteration (ΔKi67) influences disease outcomes remains unclear. Here we aim to evaluate the prognostic value of ΔKi67. Patients with paired CNB and open excision biopsy (OEB) samples between January 2009 and June 2016 were retrospectively analyzed. ΔKi67 was calculated as the absolute difference between Ki67 level in CNB and OEB samples, and the median value of 5% was adopted to category patients into high- and low ΔKi67 groups. Disease-free survival (DFS) and overall survival (OS) were compared between different ΔKi67 groups. Overall, 2173 invasive breast cancer patients were included. Median Ki67 was higher in OEB than CNB samples: 25.00% versus 20.00% (P < 0.001). Axillary nodal status, STI, histological grading, and molecular subtype were independently associated with ΔKi67 (P < 0.05). In the whole population, patients with low ΔKi67 showed superior 5-year DFS (89.6% vs 87.0%, P = 0.026), but similar OS (95.8% vs 94.3%, P = 0.118) compared to those with high ΔKi67. HER2 status at surgery was the only significant factor interacting with ΔKi67 on both DFS (P = 0.026) and OS (P = 0.007). For patients with HER2-negative disease, high ΔKi67 was associated with worse 5-year DFS (87.2% vs 91.2%, P = 0.004) as well as impaired 5-year OS (93.9% vs 96.8%, P = 0.010). ΔKi67 had no significant impact on survival of HER2-positive patients. Ki67 increase after CNB was significantly associated with worse disease outcomes in HER2-negative, but not in HER2-positive patients, which warrants further study.