The proliferation and migration of BC cells is suppressed by metformin via the dysregulation of the matrix metalloproteinases MMP-2 and MMP-9, in addition to downregulation of oncogenic microRNAs miR-21 and miR-155.98 Giles et al.99 demonstrated that metformin can decrease the size of mammary tumours and inhibit tumour formation in ovariectomised rats with 1-methyl-1-nitrosourea (MNU)-induced mammary tumours. Here, MMP2 is linked to breast cancer.