Trace elements (TEs) playing critical roles in chemical events that occur at the cellular level in the body are necessary for biological processes in human health. The role of TEs and selenoproteins and their relationship with breast cancer (BC) have not been studied thoroughly and therefore remain relatively unknown. Our study aimed to investigate possible changes in the serum selenoproteins (Glutathione Peroxidase 1 (GPX1), Glutathione Peroxidase 6 (GPX6), Selenoprotein F (Sel-F), Selenoprotein H (Sel-H), Selenoprotein S (Sel-S), Selenoprotein V (Sel-V), Selenoprotein M (Sel-M)), and TEs (Se, Zn, Mn, Cu, and Fe) levels, and TEs ratios (Fe/Se, Fe/Zn, Fe/Mn, Cu/Se, Cu/Zn, and Cu/Mn) in patients with BC before and after treatment (surgery, radiotherapy, and chemotherapy), and to evaluate the results in the patient groups with healthy controls. A total of 35 patients with BC and 25 healthy subjects were included in the study. Blood samples were collected from the patient group on the day prior to treatment, and on the day treatment was completed. Serum GPX1, GPX6, Sel-F, Sel-H, and Sel-S levels were decreased in both before and after treatment groups compared to the control. The treatment of BC resulted in increasing the concentration of Sel-V compared to before treatment levels. The treatment of BC resulted in lowering serum Se, Zn, and Fe concentrations compared to before treatment levels. Also, serum Se, Zn, and Fe levels were decreased in both before and after treatment groups compared to the control. The ratios of Cu/Se, Cu/Zn, and Cu/Mn were increased after treatment compared to the values before treatment. Cu/Se and Cu/Zn ratios were increased, but Fe/Mn ratios were decreased after treatment compared to healthy control. This study indicates that changes in serum levels of TEs such as Zn, Mn, Cu, and Se, as well as their ratios and selenoproteins, may be related to the treatments of BC. Further studies are required to clarify the exact specific mechanisms involved in the status of TEs and selenoproteins in therapeutic strategies of BC.