A leukemoid reaction is a reactive increase in the white blood cell count, which can mimic leukemia.The reaction is actually due to an infection or another disease and is not a sign of cancer.
Blood counts usually return to normal when the underlying condition is treated.
Nola M, Dotlic S. The hematopoietic and lymphoid systems. In: Damjanov I, ed. Pathology Secrets. 3rd ed. Philadelphia, PA: Elsevier Mosby; 2009:chap 9.