Cancer and diabetes, both are leading causes of mortality globally. Both the diseases are multifactorial and share number of common risk factors. Hyperglycemia and hyperinsulinemia which are the characteristic features of diabetes influences the growth rate and proliferation of tumor cells directly or indirectly. Type 2 diabetes shows stronger association with various cancers. Breast cancer is one of the malignancy affecting females worldwide. This study demonstrates that glucose not only acts as energy source in tumor cell but also acts as mitogen. Insulin not only regulates the blood glucose level but also induces growth and proliferation in MCF 7 and MDA MB 231 breast cancer cell lines independently and in combination with glucose. Metformin inhibit proliferation of MCF 7 and MDA MB 231 breast cancer cell lines independently and also in presence of glucose and insulin, but shows more inhibitory effect in presence of insulin as compare to glucose. Recently discovered insulin receptor antagonist S961 did not showed any significant response in breast cancer cell lines MCF 7 and MDA MB 231. The ineffectiveness is probably due to blocking effect of higher insulin dose. So with this investigation it can be concluded that metabolic alteration leads to proliferation of breast cancer cell lines.