Breast cancer has become the leading cause of cancer-related death among women, partly due to therapeutic resistance and treatment-related complications. Chemotherapy and hormone therapy play a crucial role in managing breast cancer patients, providing essential treatment for both disease control and overall survival. However, as new therapeutic approaches are introduced and life expectancy continues to increase, the use of these treatments has been associated with persistent adverse effects, including dyslipidemia. This article presents the case of a breast cancer patient treated with chemotherapy and tamoxifen-based hormone therapy who developed severe mixed dyslipidemia. It also reviews lipid metabolism alterations observed in breast cancer patients, emphasizing the importance of monitoring lipid levels in these patients, particularly those undergoing hormone therapy or chemotherapy, to prevent cardiovascular complications.