Taken together with our in vitro results, we demonstrated that XRCC3 expression levels affect the invasiveness of breast cancer cells, the expression/activity of targets associated with the regulation of invasiveness (i.e. TFF1), the interaction of cancer cells with the extracellular matrix (i.e. ID-1, DDR-1 and CD44) and the extracellular matrix turnover (i.e. MMP-9). The gene discussed is MMP9; the disease is breast carcinoma.