Neutrophilic leukocytosis associated with metastatic fibrosarcoma in a dog.

A 3 1/2-year-old dog with extensive tumor metastases to the lungs was found to have neutrophilic leukocytosis termed a leukemoid reaction. The term leukemoid reaction describes an absolute increase in the blood leukocyte concentration without regard to a predominant cell type or to the degree of cell immaturity. These types of reactions are extremely difficult to differentiate from leukemia. Leukemoid reactions can be acute or chronic and they may have an infectious, inflammatory, toxic, or neoplastic origin. Those reactions attributable to neoplasia have been documented in medical literature, but the mechanism causing the granulocytosis has not always been clearly understood. A granulopoietin capable of stimulating a leukemoid reaction may be elaborated by certain types of tumors, tumors with extensive metastasis, or tumors involving the lungs, liver, or stomach.