Docetaxel/cyclophosphamide (TC) is a widely used adjuvant chemotherapy regimen, especially in patients with node-negative or low-risk node-positive breast cancer. Guidelines recommend the use of prophylactic granulocyte colony-stimulating factor (G-CSF) to prevent febrile neutropenia. In this study, we aimed to explore the use of G-CSF as a primary prophylactic and determine the factors influencing its use. This retrospective study used nationwide claims data from the National Inpatient Sample compiled by the Health Insurance Review and Assessment Service in South Korea from 2018. The claims data included 10% of inpatients admitted at least once in 2018 and 1% of outpatients who were not admitted. Female patients with breast cancer who received an adjuvant TC regimen after surgery were selected. Primary prophylactic G-CSF was defined as G-CSF prescribed within two days of the first cycle of TC. The factors influencing its utilisation were investigated using the chi-square test and a multiple logistic regression model. A total of 229 patients were included in the analysis. The proportion of patients who received primary prophylactic G-CSF treatment after the first cycle of TC was 55.5%. The factors positively influencing G-CSF utilization were patients' age ≥65 years, location (i.e. metropolitan areas), and the type of healthcare facility (i.e. non-tertiary hospitals). The use of prophylactic G-CSF in patients with breast cancer who received the adjuvant TC regimen was insufficient. The use of primary G-CSF prophylaxis should be emphasised to reduce the risk of febrile neutropenia among patients receiving a myelosuppressive TC regimen.