A potential side effect of cancer patients treated with chemotherapyterm is a decrease of white blood cells. Cytotoxic chemotherapeutic agents work by destroying fast-proliferative cells. Unfortunately chemotherapy does not distinguish between normal and cancerous cells, thus normal fast-growing cells could also be destroyed. One group of cells that are affected by chemotherapy is white blood cells. White blood cells are needed by the immune system to fight infections, and the reduction in white blood cells may result in febrile neutropenia, a fever caused by reduced white blood cell count. Breast cancer patients treated with chemotherapy are often also treated with granulocyte-monocyte colony stimulating factor (GM-CSF).