Prognostic Factors Affecting Disease-Free Survival in Triple-Negative Breast Cancer and Impact of Ki-67

We aimed to investigate the prognostic factors affecting disease-free survival in patients with triple-negative breast cancer (TNBC), especially to reveal the prognostic value of Ki-67 and which cutoff value should be used. The medical records of the 180 patients who underwent surgery for invasive breast cancer were retrospectively reviewed. Potential prognostic factors that could affect the disease-free survival (DFS) in TNBC such as age (< 40, ≥ 40), grade (1, 2, 3), lymphovascular invasion (LVI) (positive, negative), perineural invasion (PNI) (positive, negative), histopathological type of tumor (invasive ductal, invasive lobular), axillary lymph node metastasis (positive, negative), number of axillary-positive lymph nodes (1–3, ≥ 4), pathological tumor size (< 2 cm, ≥ 2 cm), and Ki-67 cutoff (14%, 25%) were investigated. Univariate analysis for DFS was made by Kaplan–Meier method and comparisons were performed using log-rank test. Independent risk factors for DFS were determined by Cox proportional hazard method. The median follow-up interval was 69 months (range, 2–172). The 5-year DFS rate was 74.1%. Pathological tumor size ≥ 2 cm (HR: 7.82, 95% CI 0.14–0.34, P = 0.001), presence of axillary lymph node metastasis (HR: 8.93, 95% CI 0.15–0.66, P = 0.003), and Ki-67 cutoff of 25% (HR: 1.73, 95% CI 0.21–0.96, P = 0.040) were found to be independent prognostic factors that negatively affect DFS in TNBC. Tumor size ≥ 2 cm, axillary lymph node involvement, and Ki-67 ≥ 25% are prognostic factors that negatively affect DFS in TNBC. Post-treatment control examinations and tests should be performed at shorter intervals in TNBC patients with these characteristics.