A guanine insertion polymorphism in matrix metalloproteinase-1 promoter (MMP-1 2G) is linked to early onset and aggressiveness in cancer. We determined the role of MMP-1 2G on MMP-1 expression and breast cancer severity in patients with breast diseases. We observed no significant difference in genotype distribution among different disease groups. However, MMP-1 expression was significantly higher in atypical ductal hyperplasia than in benign breast disease and in invasive breast cancer compared to in situ breast cancer. MMP-1 2G insertion polymorphism in the invasive group also correlated significantly with the expression of MMP-1 and breast cancer prognostic markers HER2 and P53.