[Analysis of risk factors of axillary lymph node metastasis and prognosis in T1 breast cancer: a large-scale retrospective study based on the SEER database].

Objective: To analyze the clinicopathological characteristics of T1 breast cancer, the risk of lymph node metastasis and related prognostic factors. Methods: The National Cancer Institute Surveillance, Epidemiology and Results (SEER) database was utilized to search and screen out 73 421 female patients with T1 breast cancer from 2010 to 2015 for retrospective analysis. Logistic regression was used to assess the risk factors of lymph node metastasis. Kaplan-Meier survival analysis was used to analysis overall survival (OS) and breast cancer-specific survival (BCSS); Log-rank test and Cox risk model were used for prognostic analysis. Results: A total of 73 421 female patients were enrolled, including 61 955 (84.4%) N0 stage, 9 995 N1 stage (13.6%), 1 087 N2 stage (1.5%) and 384 N3 stage (0.5%). Patients with invasive cancer, histological grade 3, T1c stage, progesterone receptor (PR) positive and human epidermal growth factor receptor-2 (HER-2) positive were most likely to develop lymph node metastasis (all P <0.05). The median follow-up time was 55 months. The 5-year survival rate was 93.8%, and the 5-year BCSS rate was 98.2%. Cox regression analysis showed that T stage ( HR =1.517, 95% CI : 1.382-1.666, P <0.01), N stage ( HR =5.173, 95% CI : 4.424-6.049, P <0.01), estrogen receptor (ER) status ( HR =0.774, 95% CI : 0.607-0.987, P =0.039), PR status ( HR =0.745, 95% CI : 0.689-0.806, P <0.01) and subtype ( HR =1.439, 95% CI : 1.078-1.478, P =0.011) were independent prognostic risk factors for the OS. Histological grade ( HR =2.100, 95% CI : 1.766-2.483, P <0.01), T stage ( HR =1.310, 95% CI : 1.193-1.439, P <0.01), N stage ( HR =21.230, 95% CI : 17.980-25.060, P <0.01), PR status ( HR =0.855, 95% CI : 0.791-0.925, P <0.01) were independent prognostic risk factors for the BCSS in T1 breast cancer. Conclusions: The lymph node metastasis rate of T1 breast cancer is low and the overall prognosis is good. Pathological type, histological grade, tumor size and subtype maybe helpful in predicting the lymph node metastasis of T1 breast cancer.