Since neutropenia is one of the adverse effects of DOX administration, the aim of this study was to investigate the possibility that ABCB1 (rs10276036 C/T) and SLC22A16 (rs12210538 A/G) gene polymorphisms play a role in the development of neutropenia in Iranian breast cancer patients treated with DOX-based chemotherapy. The gene discussed is SLC22A16; the disease is neutropenia.