The prognostic and predictive potential of Ki-67 in triple-negative breast cancer

As a cell proliferation biomarker, Ki-67 is principally used in ER+/HER2- breast cancer. However, the importance and the best cutoff point of Ki-67 in triple-negative breast cancer (TNBC) remains unclear and was evaluated in this study.A total of 1800 patients with early invasive TNBC between 2011 and 2016 at Fudan University Shanghai Cancer Center were consecutively recruited for this study. The optimal cutoff for Ki-67 was assessed by Cutoff Finder. Propensity score matching (PSM, ratio = 1:2) was performed to match the Ki-67^low group with the Ki-67^high group. Overall survival (OS) and disease-free survival (DFS) were compared between the two groups using the Kaplan-Meier method and Cox regression model. The most relevant cutoff value for Ki-67 for prognosis was 30% (p = 0.008). At the cutoff point of 30%, worse DFS and OS were observed in the Ki-67^high group. In multivariate analyses, N-stage (p < 0.001), T-stage (p = 0.038), and Ki-67 at the 30% threshold (p = 0.020) were independently linked to OS. In subgroup analysis, Ki-67 cutoff at 30% had prognostic and predictive potential for DFS with either tumor size ≤2 cm (p = 0.008) or lymph node-negative (N-) (p = 0.038) and especially with T₁N₀M₀ (stage I) TNBCs. For 945 N- TNBC patients, adjuvant chemotherapy (CT) was associated with better OS in the Ki-67^high group (p = 0.017) than in the Ki-67^low group (p = 0.875). For stage I/Ki-67^low patients, adjuvant CT did not affect DFS (p = 0.248). Thus, Ki-67 cutoff at 30% had early independent prognostic and predictive potential for OS and DFS in TNBCs, and Ki-67 > 30% was significantly associated with worse prognosis, especially for stage I patients. For stage I/Ki-67^low TNBC patients, the advantage of CT is unclear, providing the basis for future de-escalation therapy.