Breast cancer has emerged as the most commonly diagnosed cancer in Argentina, with an incidence of 21,631 new cases reported in 2022. Chemoprevention strategies aim to reduce the risk of developing invasive breast cancer, and chemotherapy remains a primary treatment for metastatic cases, particularly in triple-negative breast cancer (TNBC). However, metal-based drugs like cisplatin, commonly used in chemotherapy, exhibit significant side effects and the potential for resistance with prolonged use. Recent research has explored the combination of metal complexes with amino acids to enhance pharmacokinetic properties and reduce toxicity. In this context, we investigated the effects of two copper complexes with neocuproine [CuCl2(neo)] (1) and compared with a ternary complex with a dipeptide (alanine and phenylalanine) [Cu(ala-phe)(neo)]·4H2O (2) in two human breast cancer cell lines (MCF-7 and MDA-MB-231). Notably, both complexes demonstrated IC50 values below 3 μM and clonogenic inhibition in both cell lines. However, the mechanisms of action varied according to the cell line. In MCF-7, direct DNA damage was observed using the comet assay, while in the MDA-MB-231 cell line, reactive oxygen species (ROS) production occurred. Additionally, late apoptosis and necrosis were induced by complex 2 in MCF-7, and necrosis in MDA-MB-231 (preliminary data). Furthermore, exhibited migration inhibition in both cell lines. These promising results suggest that the ternary copper complex 2 warrants further evaluation as an alternative therapeutic approach for breast cancer treatment.