RÉSUMÉ
Neutrophilic leukocytosis above 50 × 10/l not involving the bone marrow, defines a leukemoid reaction (LR). Although it simulates leukemia, most of the causes are inflammatory and benign. LR has been found to be associated with malignancy which is postulated to be caused by granulocyte colony-stimulating factor (G-CSF) secreted by the tumor cells. A 50 years old woman, presented with high grade infiltrating ductal carcinoma of breast and leukocytosis (60 ×10/ cumm). After completion of MRM, the condition of neutrophilic leukocytosis subsided. After three months, total leukocyte count rose and local relapse of tumor was found. Following that wide excision was done,and the condition of leukocytosis subsided again. In this case the leukemoid reaction was a paraneoplastic reaction which can be view as a potential for prognostic marker.