Breast cancer is estimated to account for 31% new onset female cancers. Matrix metalloproteinases (MMPs) are extracellular zinc-dependent endopeptidases involved in the degradation and remodeling of extracellular matrix in physiological and pathological processes. In this study, we aimed to evaluate the use of matrix metalloproteinase-13 (MMP-13) as a potential tumor marker in breast cancer and we also aimed to investigate the role of infection as a cause of carcinogenesis by estimating the incidence of anti-cytomegalovirus IgG antibodies in breast cancer patients. Subjects and Methods: Serum CA15.3, anti-CMV IgG and MMP-13 were measured in 50 breast cancer female patients, 20 female patients with fibroadenoma of breast and 20 healthy age-matched female volunteers. Results: MMP-13 levels showed no significant difference between breast cancer patients and controls; on the other hand MMP-13 levels were significantly higher in fibroadenoma patients compared to controls. CA15.3 levels were significantly higher in breast cancer cases compared to both fibroadenoma and healthy controls. Conclusion: The results of this study show that MMP-13 level is highest among control group, while fibroadenoma group had the lowest MMP-13 level. CA15.3 is still the most useful serum tumor marker in patients with breast cancer.