BACKGROUND: Guidelines recommend primary prophylactic use of colony-stimulating factor (PP-CSF) when risk of febrile neutropenia (FN)-based on chemotherapy and patient risk factors-is high. Whether and how PP-CSF use may have changed over time (e.g., due to guideline revisions, increasing use of myelosuppressive regimens, controversy regarding inappropriate CSF use), and whether there has been a concomitant change in the incidence of FN, is unknown. METHODS: A