Chemotherapy-induced neutropenia often occurs in our routine work and presents an obstacle for adequate (dose and continuance) treatment, which may affect patients' outcome. Granulocyte colony-stimulating factors (GCSFs) effectively prevent myelosuppression and thus improve the standard treatment. Through their application cases of chemotherapy-induced neutropenia have been reduced. Still these factors cannot remove entirely the danger of encountering neutropenia, which can cause dangerous complications. We present a case of a fulminate anaerobic infection with unknown origin in a patient with metastatic breast cancer after standard treatment with chemotherapy supported by GCSFs.