BACKGROUND: Breast cancer is the most commonly diagnosed female cancer and is a major cause of cancer-related deaths in women. Triple-negative breast cancer (TNBC) is defined as ER, PR and HER2 negative, which are characterized by rapid progression with low survival rates with limited therapeutic choices. Polo-like kinase 1 protein acts as a cell division regulator which is highly expressed in many tumors making it a potentially valuable target for antiproliferative therapies. In this study we tried to evaluate the value of this marker as a possible therapeutic target in TNBC. METHODS: This research studied the immunohistochemical expression of PLK1 done on 49 paraffin blocks of TNBC female patients and then correlated with the different clinicopathological parameters. RESULTS: Our results showed high PLK1 expression in 91.9% of cases. Most of the high grade tumors showed high PLK1 high score (76.9%). All cases showing lymph node metastasis showed high PLK1 expression, implying a statistically significant correlation between PLK1 expression and tumor grade as well as N stage. CONCLUSION: PLK1, although a negative prognostic factor, but is a promising therapeutic target for treating TNBC patients.