The most common cause of death in women is breast cancer and the emergence of its associated bone metastasis. Development of bone metastases cause bone loss, severe pain, nerve compression, spinal instability and hypercalcemia. Considering this health problem in terms of morbidity and mortality, it is necessary to discover new drug. Drugs can affect bone cells, tumor cells and interaction between tumor and bone cells. Verron et al (2010) showed that Ga inhibits formation, differentiation and resorption activity of osteoclasts in a dose – dependent manner, without affecting their viability. The aim of the present study is to evaluate Ga effect on tumor cells by using breast carcinoma cell lines (MRMT – 1 and MDA – MB - 231). After three days of treatment, 100 µM Ga significantly decreases both the viability and proliferation of MRMT - 1 by 40 % and 60 % respectively. Also, we found that Ga decreases expression of osteoblastic genes (OPN, Runx2 and BMP2) and angiogenic factor VEGF. Unfortunately, we didn’t confirm these deleterious effects on human carcinoma breast cell line. To mimic the pathophysiological microenvironment of bone metastasis, we established a co – culture model based on treating monocytic RAW 264.7 cells with RANKL and conditioned medium isolated form culture of MDA – MB – 231 cells previously stimulated with TGF – β. We showed that Ga decreases differentiation of RAW 264.7 cells in a dose – dependent manner. These interesting results are preliminary and it is necessary to repeat and to confirm them.