Background and Aims T1 stage breast cancer patients have an overall favorable prognosis, but there is still a small subset of patients who exhibit high invasiveness and are prone to adverse outcomes such as recurrence, metastasis, and death, leading to a poorer prognosis. This study was conducted to investigate the clinicopathologic characteristics that influence T1 stage breast cancer and determine the risk factors associated with prognosis, for early identification of high-risk T1 stage breast cancer patients and providing reference for clinical decision-making.Methods The data of 1 250 patients with primary invasive breast cancer at stages T1 to T3 who underwent surgical treatment at Xiangya Hospital, Central South University, from January 2011 to December 2015 were retrospectively analyzed. The differences in clinicopathologic characteristics between T1 and non-T1 stage patients were determined. Univariate and multivariate Cox regression models were used to analyze the risk factors affecting recurrence, metastasis, and death in T1 stage breast cancer patients. The Kaplan-Meier method was employed to assess the differences in overall survival (OS) and disease-free survival (DFS) among T1 stage breast cancer patients with different risk factors, and the Log-rank test was used to compare the survival curves between groups.Results Among the 1 250 patients with primary invasive breast cancer, there were 261 cases (20.88%) at stage T1 and 989 cases (79.12%) at non-T1 stage (T2 and T3). Compared to non-T1 stage patients, T1 stage patients had lower BMI value, fewer axillary lymph node metastases, fewer unfavorable biological characteristics, and better survival prognosis (all P<0.05). During the follow-up period, there were 15 deaths and 40 cases of recurrence and metastasis among T1 stage patients. The median OS was 94 (5-132) months, with 2-, 5-, and 10-year OS rates of 97%, 95%, and 94%, respectively. The DFS was 92 (4-138) months, with 2-, 5-, and 10-year DFS rates of 95%, 88%, and 82%, respectively. The results of the multivariate Cox regression model indicated that lymph node metastasis (HR=4.904, 95% CI=1.588-15.144, P=0.006) and unfavorable biological characteristics (HR=4.241, 95% CI=1.433-12.552, P=0.009) were independent risk factors for OS in T1 stage patients. Lymph node metastasis (HR=3.118, 95% CI=1.553-6.262, P=0.001), unfavorable biological characteristics (HR=2.295, 95% CI=1.034-5.093, P=0.041), and Ki-67>14% (HR=2.258, 95% CI=1.079-4.723, P=0.031) were independent risk factors for DFS in T1 stage patients. Survival analysis showed that among T1 stage patients with positive lymph node metastasis, those with favorable biological characteristics had no significant difference in OS and DFS compared to patients with negative lymph node metastasis (both P>0.05), while those with adverse biological characteristics had the worst OS and DFS (both P<0.05).Conclusion Overall, T1 stage invasive breast cancer patients have a relatively good prognosis. However, axillary lymph node metastasis and unfavorable biological characteristics are risk factors for early recurrence, metastasis, and death in T1 stage breast cancer patients. The combination of biological characteristics can further identify high-risk patients with T1 stage breast cancer and positive axillary lymph nodes, providing reference for treatment decisions in T1 stage breast cancer.