Aim: Determination of cut-off value for Ki67 index, it’s corelation in luminal breast carcinoma with patient’s age, tumor size, histological grade (HG), and expression of estrogen (ER) and progesterone (PR). Introduction: Breast cancer is a heterogeneous disease characterized by different morphology, immunohistochemical profile, clinical course and response to applied therapy. Ki67 proliferative index is one of the prognostic and predictive factors, whose methodological determination and analysis are still unstandardized. Material and Methods: Retrospectively, we analysed 120 pathohistological reports of patients who were treated in the period 01.01.2009. until 31.12.2011. at the Oncology Institute of Vojvodina, and to whom immunohistochemistry was proven luminal breast cancer (positive ER and PR, negative HER2), without axillary lymph node metastases. Results: The average patient’s age was 57.42±10.17 years; average tumor size 17.98±6.97mm; recurrence was registered in 8 (6.7%) patients with average recurrence time of 49±20.23 months. “Cut off” Ki67 value of prognostic significance for period without recurrence is 20.75%. For correlation testing χ2 and Kendal τ-b tests were used. It’s shown unsignificant relationship between Ki67 and patient’s age (p=0.401 and p=0.293), as well as the strength of expression ER (p=1.00, p=0.957) and PR (p=0.273, p=0.189). Significant correlation is present for Ki67 with size (p=0.035, p=0.20) and tumor’s HG (p=0.041, p=0.20). Conclusion: Breast carcinoma is heterogeneous disease, so it’s difficult to predict its course and outcome using standard histopathological factors and biomarkers. For prognostic-predictive purposes, it’s necessary to include additional biomarkers, where Ki67 stands out above all, whose high value correlates with factors of bad prognosis.

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