Abstract
BACKGROUND: Younger and older patients with breast cancer often present with different clinicopathological characteristics and exhibit different risk factors for recurrence. This study sought to evaluate the biological characteristics and identify the recurrence risk factors in patients with operable breast cancer who were ≤40 years of age. METHODS: This retrospective study investigated the biological characteristics and clinical outcomes of young patients (aged ≤40 years) with operable breast cancer who had been admitted to the Second Affiliated Hospital of Soochow University for treatment from January 2015 to December 2019. Clinicopathological and follow-up data were collected and statistically analyzed using IBM SPSS 27.0 software. The disease-free survival (DFS) rates were evaluated, and regression analyses were conducted to identify risk factors associated with adverse outcomes. RESULTS: A total of 154 young patients (aged ≤40 years) with operable breast cancer were included in this study, of whom 68 (44.2%) were aged ≤35 years. In terms of breast cancer subtypes, there were 19 (12.3%) patients with luminal A-like disease, 74 (48.1%) patients with luminal B-like disease, 17 (11.0%) patients with human epidermal growth factor receptor 2 (HER2)-positive (non-luminal) disease, and 44 (28.6%) patients with triple-negative breast cancer (TNBC). The 5-year DFS rate of all the patients was 88%; among those with TNBC, the rate was slightly lower at 76%. According to the results of the log-rank test, tumor (T) stage, node (N) status (N0 or N+), the biological subtype, and the Ki-67 index (with a 14% cut-off value between high and low expression levels) were risk factors for recurrence. The Cox regression analysis showed that the biological subtype was the only risk factor for recurrence. The multiple linear regression analysis demonstrated that the pathological type, tumor grade, estrogen receptor (ER) labeling intensity, and progesterone receptor (PR) expression level significantly affected the level of Ki-67 expression. CONCLUSIONS: This retrospective study showed that biological subtype was the most important risk factor for recurrence in operable breast cancer patients ≤40 years. The Ki-67 index is influenced by the pathological type, primary tumor grade, ER labeling intensity, and PR expression level. Fourteen percent is recommended as the cut-off value for the high and low expression of Ki-67 in clinical practice.