White blood cell growth factors, also known as hematopoietic (blood-forming) colony-stimulating factors (CSFs), are proteins that help the body produce white blood cells. White blood cells help fight infection and can be destroyed during some types of cancer treatment. Having low numbers of white blood cells is called neutropenia, and patients with neutropenia are more likely to develop infections. Neutropenia may occur with or without a fever. Febrile neutropenia (neutropenia with a fever) may be a sign that the patient has developed an infection and requires antibiotics and hospitalization. ASCO recommends that patients avoid febrile neutropenia because of the risk of serious complications.

CSFs are supportive medications, which mean that they are not intended to treat cancer, but rather to prevent patients from developing side effects of cancer treatment, such as infections. CSFs are given as shots, usually 24 hours after a chemotherapy treatment, and include filgrastim (Neupogen), sargramostim (Leukine), and pegfilgrastim (Neulasta). These medications are made in the laboratory and are similar to those naturally produced by the body.