e22184 Background: Breast cancer (BC) is the most common tumor in Mexican women between 35 to 50 years old. KI67 is a nuclear antigen considered as a proliferation marker with potential prognostic significance in BC survival. Objective: To determine the correlation between KI67 and prognostic factors in BC patients (pts). Methods: Of 340 consecutive BC pts seen from January 2000 to September 2008, pts with invasive BC that have a complete IHC assay determination were analyzed (estrogen receptor [ER], progesterone receptor [PR], HER2, p53, KI67). KI67 was determined by monoclonal antibody MIB-1. Patients ´s clinical characteristics and tumor immunohistochemical factors were registered. Patients were divided into 4 groups according to KI67 levels: 1) KI67 < 5%, 2) 6 to 20%, 3) 21 to 50% and 4) > 51%. Descriptive statistical methods and X2, ANOVA tests were used. Results: 154 pts analyzed, mean age 53.5 ± 12 yrs, range 28 -83, median KI67: 25, (0 - 95%). Group 1: 22 pts (14.3%), Group 2: 52 (33.8%); group 3: 49 (31.8%), group 4: 31 pts (20.1%). Median KI67 by group: 5, 15, 30 70%. Among pts with KI67 > 51% we observed: higher proportion of advanced stages (III-IV) [27.3%, 7.7%, 25.6%, 38.7% (p= 0.027)], positive lymph nodes (59%, 25%, 42.8% 70.9%, [p=0.003]), ER negative (27.3%, 5.8%, 28.4%, 51.7% [p= 0.000]), PR negative (36.4%, 26.9%, 22.5%, 61.3%; [p= 0.003]); P53 +ve (9.1%, 71.1%, 73.4%, 77.4%; [p= 0.028]), angiogenesis [> 15 vessels × field] (31.8%, 21.1%, 24.5%, 54.5%; [p=0.006])), triple negative phenotype (4.5%; 3.8%, 10.2%, 41.9%; [p=0.000]). We do not observe correlation among KI67 status age, tumor size and HER2 (p > 0.05). Conclusions: High cellular proliferation through KI 67 (> 51%) was related to poor prognostic factors in BC. No significant financial relationships to disclose.