Background: Current understanding of tumor biology suggests that breast cancer is a group of diseases with different intrinsic molecular subtypes. Anatomic staging system alone is insufficient to provide future outcome information. The American Joint Committee on Cancer (AJCC) expert panel updated the 8th edition of the staging manual with prognostic stage groups by incorporating biomarkers into the anatomic stage groups. In this study, we retrospectively analyzed the data from our center in China using the anatomic and prognostic staging system based on the AJCC 8th edition staging manual. Methods: We reviewed the data from January 2008 to December 2014 for cases with Luminal B Human Epidermal Growth Factor Receptor 2 (HER2)?negative breast cancer in our center. All cases were restaged using the AJCC 8th edition anatomic and prognostic staging system. The Kaplan?Meier method and log?rank test were used to compare the survival differences between different subgroups. SPSS software version 19.0 (IBM Corp., Armonk, NY, USA) was used for the statistical analyses. Results: This study consisted of 796 patients with Luminal B HER?negative breast cancer. The 5?year disease?free survival (DFS) of 769 Stage Ⅰ–Ⅲ patients was 89.7%, and the 5?year overall survival (OS) of all 796 patients was 91.7%. Both 5?year DFS and 5?year OS were significantly different in the different anatomic and prognostic stage groups. There were 372 cases (46.7%) assigned to a different group. The prognostic Stage Ⅱ and Ⅲ patients restaged from anatomic Stage Ⅲ had significant differences in 5?year DFS ( χ2 = 11.319, P = 0.001) and 5?year OS ( χ2 = 5.225, P = 0.022). In addition, cases restaged as prognostic Stage Ⅰ, Ⅱ, or Ⅲ from the anatomic Stage Ⅱ group had statistically significant differences in 5?year DFS ( χ2 = 6.510, P = 0.039) but no significant differences in 5?year OS ( χ2 = 5.087, P = 0.079). However, the restaged prognostic Stage Ⅰ and Ⅱ cases from anatomic Stage Ⅰ had no statistically significant differences in either 5?year DFS ( χ2 = 0.440, P = 0.507) or 5?year OS ( χ2 = 1.530, P = 0.216). Conclusions: The prognostic staging system proposed in the AJCC 8th edition refines the anatomic stage group in Luminal B HER2?negative breast cancer and will lead to a more personalized approach to breast cancer treatment.