CSF2 and breast cancer: It is considered an effective and relatively safe supportive care medication; however, it can cause rare and serious side effects such as spleen rupture or infarction.<h4>Case presentation</h4>We are reporting a case of a 27-year-old female with breast cancer who has been treated with dose-dense chemotherapy and received colony-stimulating factor as primary prevention of febrile neutropenia that was complicated halfway through with splenic infarction.