Background and Aims: The age of onset has a certain association with the prognosis of a number of tumors, but there are obvious differences among different tumors, even among different subtypes of the same cancer. Triple-negative breast cancer (TNBC), as a poor prognostic subtype of breast cancer, has always been an important concern. This study was to designated to analyze the relationship between age and the prognosis of the TNBC patients. 
Methods: According to the inclusion and exclusion criteria, the clinical data of 317 patients with stage I-III TNBC undergoing surgery in Peking Union Medical University Hospital from January 2011 to December 2014 were collected for a retrospective study. The whole cohort were divided into ≤40 years old group and >40 years old group according to the age of onset of the patients. The differences in clinicopathologic characteristics, local-regional recurrence-free survival (LRRFS), distance metastasis-free survival (DMFS), disease-free survival (DFS) and overall survival (OS) between the two groups of patients were compared, and the factors including age affecting the DFS and OS of the TNBC patients were analyzed. Further, the differences in age and other clinicopathologic factors between patients with early distant metastasis (DM) and late DM were compared.
Results: In terms of clinicopathologic features, the histological grade was poorer, the incidence of  vessel tumor embolus was higher, tumor stage was more advanced and the proportions of cases receiving chemotherapy and radiotherapy were higher in ≤40 years old group than those in >40 years old group (all P<0.05). Survival analysis showed that the DMFS (64.3% vs. 83.2%), DFS (55.7% vs. 79.2%) and OS (71.8% vs. 86.2%) were worse in ≤40 years old group than those in >40 years old group (all P<0.05), while there was no statistical difference in LRRFS between the two groups (87.5% vs. 94.9%, P>0.05). Both age ≤40 years and number of positive lymph nodes ≥4 were independent risk factors for the prognosis of TNBC patients (DFS: HR=1.983, 95% CI=1.280–3.071, P=0.002; HR=2.064, 95% CI=1.091–3.904, P=0.026; OS: HR=1.799, 95% CI=1.052–3.076, P=0.032; HR=4.062, 95% CI=1.841–8.963, P=0.001). Age showed no significant influence on the early or late occurrence of DM (P>0.05).
Conclusion: Age is an independent risk factor for poor prognosis in TNBC patients. Patients with age ≤ 40 years old at the time of diagnosis may face worse outcomes than those over 40 years old. Therefore, more attention should be paid to the young TNBC patients, for whom, more rigorous treatment and follow-up plan should be made to realize a patient-tailored precision therapeutic strategy.